US-led strikes against ISIS kill more than 170 Raqqa civilians, sources say

AMMAN, Aug 22 (Reuters) - More than 170 civilians have been killed by U.S.-led strikes on Islamic State in Raqqa city in the past week, a spike in casualties since an offensive to oust the militants began more than two months ago, a war monitor and sources said.

The U.S.-led coalition against Islamic State said attacks on militant targets were conducted routinely and the allegation had been sent to their teams for assessment.

The monitoring group Syrian Observatory for Human Rights said at least 42 people, including 19 children and 12 women, were killed on Monday in strikes that destroyed buildings where families were sheltering.

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Syrian men stand at the site of a car bomb explosion in the al-Zahraa neighborhood in Homs on October 29, 2014. At least 37 people, including children, were injured in the attack on the government-controlled neighbourhood in the central Syrian city of Homs, state television reported. The majority of Al-Zahraa's residents are Alawite, the same sect as President Bashar al-Assad. AFP PHOTO/ STR (Photo credit should read STR/AFP/Getty Images)
A poster of Syrian President Bashar al-Assad adorns a wall as the vehicle of United Nations special envoy for Syria Staffan de Mistura leaves his hotel on November 9, 2014 in the capital Damascus. De Mistura is expected to meet Bashar al-Assad to relaunch peace efforts in the country ravaged by close to four years of civil war. AFP PHOTO/ LOUAI BESHARA (Photo credit should read LOUAI BESHARA/AFP/Getty Images)
ALEPPO, SYRIA - NOVEMBER 08: Armed members of Islamic Front stand guard at their positions during clashes between the Islamic State of Iraq and the Levant (ISIL) and troops of Islamic Front in the Mari district of Aleppo, Syria, on November 8, 2014. (Photo by Ahmed Muhammed Ali/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - NOVEMBER 09: Members of Civil Defense team try to rescue the people from the debris of a building in the Al-Bab district of Aleppo, Syria, on November 9, 2014. After a helicopter of Syrian army attacked with a barrel bomb on the Al-Bab district of Aleppo which is under control of the Islamic State of Iraq and the Levant (ISIL), 10 people killed and 25 others were injured. (Photo by Stringer/Anadolu Agency/Getty Images)
KOBANI, SYRIA - NOVEMBER 8: Armed Kurdish fighters are seen during the clashes with Islamic State of Iraq and Levant (ISIL) members in Kobani (Ayn al-Arab), Syria on November 8, 2014. According to the armed groups the movement of the ISIL is slow downed after the US-led coalition airstrikes and with the support of Free Syrian Army members and Kurdish Peshmerga forces in Kobani. (Photo by Ahmed Deeb/Anadolu Agency/Getty Images)
A picture taken from the Israeli-annexed Golan Heights shows smoke billowing near the Syrian village of Jubata al-Khashab following an explosion during fighting between forces loyal to Syrian President Bashar Assad and rebel fighters, on September 23, 2014. Israel will respond 'forcefully' to attempts to threaten its security, Defence Minister Moshe Yaalon warned, after it shot down a Syrian warplane over the Golan Heights. AFP PHOTO/ JALAA MAREY (Photo credit should read JALAA MAREY/AFP/Getty Images)
Smoke rises from the Syrian Syrian village of Jubata al-Khashab after it was bombed by a Syrian fighter jet on September 23, 2014, moments before the jet was shot down by the Israeli military over the Golan Heights. Israel shot down a Syrian fighter jet over the Golan Heights, the army said, indicating that it had crossed the ceasefire line into the Israeli-occupied sector. It was the most serious incident to take place on the strategic plateau since the outbreak of the Syrian civil war in 2011. AFP PHOTO/ JALAA MAREY (Photo credit should read JALAA MAREY/AFP/Getty Images)
A Syrian fighter jet is seen in flames after it was hit by the Israeli military over the Golan Heights on September 23, 2014. Israel shot down a Syrian fighter jet over the Golan Heights, the army said, indicating that it had crossed the ceasefire line into the Israeli-occupied sector. It was the most serious incident to take place on the strategic plateau since the outbreak of the Syrian civil war in 2011. AFP PHOTO/ JALAA MAREY (Photo credit should read JALAA MAREY/AFP/Getty Images)
Smoke rises from the Syrian village of Jubata al-Khashab after it was bombed by a Syrian fighter jet on September 23, 2014, moments before a Syrian jet was shot down by the Israeli military over the Golan Heights. Israel shot down a Syrian fighter jet over the Golan Heights, the army said, indicating that it had crossed the ceasefire line into the Israeli-occupied sector. It was the most serious incident to take place on the strategic plateau since the outbreak of the Syrian civil war in 2011. AFP PHOTO/ JALAA MAREY (Photo credit should read JALAA MAREY/AFP/Getty Images)
A Syrian fighter jet is seen in flames after it was hit by the Israeli military over the Golan Heights on September 23, 2014. Israel shot down a Syrian fighter jet over the Golan Heights, the army said, indicating that it had crossed the ceasefire line into the Israeli-occupied sector. It was the most serious incident to take place on the strategic plateau since the outbreak of the Syrian civil war in 2011. AFP PHOTO/ JALAA MAREY (Photo credit should read JALAA MAREY/AFP/Getty Images)
A convoy of United Nations Disengagement Observer Force (UNDOF) vehicles is seen as it leaves the Syrian side of the Golan Heights into the Israeli-occupied side of the strategic plateau, on September 15, 2014. Troops of the UNDOF were withdrawing from the Syrian part of the Golan Heights due to security reasons. The UNDOF is monitoring a 1974 ceasefire agreement between Israel and Syria on the Golan Heights. AFP PHOTO / JALAA MAREY (Photo credit should read JALAA MAREY/AFP/Getty Images)
Israeli soldiers block a main road near the Quneitra border crossing in the Israeli-occupied Golan Heights on September 1, 2014 , following heavy fighting between Syrian government troops and opposition forces in Syrian territory, near the Quneitra crossing. Israel downed a drone over the occupied Golan Heights yesterday, the army said, amid mounting tension on the UN-patrolled armistice line with Syria on the strategic plateau. AFP PHOTO /MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
A picture taken from the Israeli-annexed Golan Heights, shows a group of rebel fighters walking behind the Israeli border with Syria near the Quneitra border crossing, on the Syrian side of the Golan, on September 2, 2014. The unrest on Israel's doorstep followed a spillover of mortar and gunfire into Israeli-controlled territory, putting the Jewish state on high alert and prompting it to shoot down a drone over the occupied plateau. AFP PHOTO/ MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
Israeli soldiers block a main road near the Quneitra border crossing in the Israeli-occupied Golan Heights on September 1, 2014 , following heavy fighting between Syrian government troops and opposition forces in Syrian territory, near the Quneitra crossing. Israel downed a drone over the occupied Golan Heights yesterday, the army said, amid mounting tension on the UN-patrolled armistice line with Syria on the strategic plateau. AFP PHOTO /MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
Israeli soldiers block a main road near the Quneitra border crossing in the Israeli-occupied Golan Heights on September 1, 2014 , following heavy fighting between Syrian government troops and opposition forces in Syrian territory, near the Quneitra crossing. Israel downed a drone over the occupied Golan Heights yesterday, the army said, amid mounting tension on the UN-patrolled armistice line with Syria on the strategic plateau. AFP PHOTO /MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
In a picture taken from the Israeli-annexed Golan Heights, smoke billows from the Syrian village of Quneitra following an explosion during fighting, between forces loyal to Syrian President Bashar Assad and rebels, near the Quneitra border crossing on August 31, 2014. Heavy fighting between Syrian government troops and opposition forces overflowed into the buffer zone separating Syrian and Israeli-occupied territory over the weekend. AFP PHOTO/ MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
Members of United Nations Disengagement Observer Force (UNDOF) use binoculars to watch the Syrian side of the Golan Heights at Mount Bental near the Quneitra border crossing in the Israeli occupied Golan Heights on August 31, 2014. Heavy fighting between Syrian government troops and opposition forces flowed into the buffer zone separating Syrian and Israeli-occupied territory at the weekend. Dozens of Filipino UN peacekeepers escaped the hot zone overnight after rebels rammed their Golan Heights outpost with armed trucks, the Philippine military said. AFP PHOTO/ MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
In a picture taken from the Israeli-annexed Golan Heights, smoke billows from the Syrian village of Quneitra following an explosion during fighting, between forces loyal to Syrian President Bashar Assad and rebels, near the Quneitra border crossing on August 31, 2014. Heavy fighting between Syrian government troops and opposition forces overflowed into the buffer zone separating Syrian and Israeli-occupied territory over the weekend. AFP PHOTO/ MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
An Irish member from the United Nations Disengagement Observer Force (UNDOF) sits in an armoured personnel carrier as he maneuvers, near the border of Syrian territory, close to the town of Buqaata in the Israeli-annexed Golan Heights on August 31, 2014. Heavy fighting between Syrian government troops and opposition forces flowed into the buffer zone separating Syrian and Israeli-occupied territory at the weekend. Dozens of Filipino UN peacekeepers escaped the hot zone overnight after rebels rammed their Golan Heights outpost with armed trucks, the Philippine military said. AFP PHOTO/ MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
Irish members from the United Nations Disengagement Observer Force (UNDOF) convoy maneuver, near the border of Syrian territory, close to the town of Buqaata in the Israeli-annexed Golan Heights on August 31, 2014. Heavy fighting between Syrian government troops and opposition forces flowed into the buffer zone separating Syrian and Israeli-occupied territory at the weekend. Dozens of Filipino UN peacekeepers escaped the hot zone overnight after rebels rammed their Golan Heights outpost with armed trucks, the Philippine military said. AFP PHOTO/ MENAHEM KAHANA (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
A picture taken in the Israeli-occupied Golan Heights on August 31, 2014, shows members of United Nations Disengagement Observer Force (UNDOF) using binoculars to watch the Syrian side of the Golan Heights near the Quneitra border crossing. Some of the UNDOF peacekeepers caught up in heavy fighting on the Golan Heights reached safety after the rebels, some linked to Al-Qaeda, surrounded them and demanded their weapons. AFP PHOTO / JALAA MAREY (Photo credit should read MENAHEM KAHANA/AFP/Getty Images)
Israeli soldiers patrol on the Israeli-occupied Golan Heights near the Quneitra crossing, the only border crossing between Israel and Syria, on August 30, 2014. Philippine UN peacekeepers in the Golan Heights clashed with Syrian rebels, Philippine Defence Minister Voltaire Gazmin said in Manila, after Syrian rebels, including fighters from the Al-Qaeda affiliate Al-Nusra Front, stormed the Golan Heights crossing on August 27, surrounding 70 Filipino UN Peacekeepers. AFP PHOTO/ AHMAD GHARABLI (Photo credit should read AHMAD GHARABLI/AFP/Getty Images)
Irish members of the United Nations Disengagement Observer Force (UNDOF) sit on their armoured vehicles in the Israeli-annexed Golan Heights as they wait to cross into the Syrian-controlled territory, on August 28, 2014. The UN has confirmed that 43 UN peacekeepers were seized in the Syrian Golan. AFP PHOTO / JACK GUEZ (Photo credit should read JACK GUEZ/AFP/Getty Images)
Syrian civil defense workers rescue a man from under the rubble, on July 25, 2014, after a Syrian government helicopter allegedly dropped a barrel bomb on the Sakhour eastern neighborhood, in the northern city of Aleppo. Dozens of people have been killed in 24 hours of clashes in northern Syria between regime forces and jihadist militants, the Syrian Observatory for Human Rights said. AFP PHOTO / AMC / ZEIN AL-RIFAI (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)
ARSAL, LEBANON - AUGUST 19: Syrian refugee kids are seen at Arsal district where more than a hundred thousand of Syrians, fled from the civil war in their country, are stuck due to the clashes between Lebanese army, Al-Nusra Front and Islamic State, IS,-led terrorist groups, in Arsal, Lebanon on August 19, 2014. (Photo by Ayse Sarioglu/Anadolu Agency/Getty Images)
ARSAL, LEBANON - AUGUST 19: A Syrian refugee kid is seen at Arsal district where more than a hundred thousand of Syrians, fled from the civil war in their country, are stuck due to the clashes between Lebanese army, Al-Nusra Front and Islamic State, IS,-led terrorist groups, in Arsal, Lebanon on August 19, 2014. (Photo by Ayse Sarioglu/Anadolu Agency/Getty Images)
ARSAL, LEBANON - AUGUST 19: A Syrian refugee kid's feet are seen at Arsal district where more than a hundred thousand of Syrians, fled from the civil war in their country, are stuck due to the clashes between Lebanese army, Al-Nusra Front and Islamic State, IS,-led terrorist groups, in Arsal, Lebanon on August 19, 2014. (Photo by Ayse Sarioglu/Anadolu Agency/Getty Images)
ARSAL, LEBANON - AUGUST 19: A Syrian refugee kid plays at Arsal district where more than a hundred thousand of Syrians, fled from the civil war in their country, are stuck due to the clashes between Lebanese army, Al-Nusra Front and Islamic State, IS,-led terrorist groups, in Arsal, Lebanon on August 19, 2014. (Photo by Ayse Sarioglu/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - AUGUST 12: A Syrian kid is rescued from the wreckage by civil defence members following Syrian regime helicopters dropped barrel bombs on Bab al-Nairab district of Aleppo, Syria on August 12, 2014. (Photo by Syrian Civil Defense/Pool/Anadolu Agency/Getty Images)
Syrian civil defence workers rescue a man from under the rubble of a building following a reported barrel-bomb attack by Syrian government forces on August 11, 2014 in the Bab al-Neirab neighbourhood of the northern Syrian city of Aleppo. Last month Human Rights Watch said the number of rebel sectors hit by barrel bombs had almost doubled in five months. AFP PHOTO / ZEIN AL-RIFAI (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)
SULAYMANIYAH, IRAQ - JULY 28: Eid al-Fitr is a special celebration for the Muslims, but for Syrian refugee children in a refugee camp, it's a bittersweet time because of the ongoging civil war in their country in Sulaymaniyah, Iraq on July 28, 2014. (Photo by Feriq Ferec/Anadolu Agency/Getty Images)
SULAYMANIYAH, IRAQ - JULY 28: Eid al-Fitr is a special celebration for the Muslims, but for Syrian refugee children in a refugee camp, it's a bittersweet time because of the ongoging civil war in their country in Sulaymaniyah, Iraq on July 28, 2014. (Photo by Feriq Ferec/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JULY 28: In spite of Syrian civil war, Syrian muslims celebrate Eid al-Fitr holiday that marks the end of the holy fasting month of Ramadan on July 28, 2014 in Aleppo, Syria. During normal times, families in Syria would be busy now with preparations for Eid al-Fitr and visiting each other, the three-day holiday marking the end of the Muslim fasting month of Ramadan. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JULY 20: A member of Syrian Islamic Front digs a tunnel that used to explode military quarters of Syrian regime in Aleppo, Syria on July 20, 2014. As the Syrian civil-war continues, they mined a half-mile underground-tunnel, filled it with explosives during ongoing struggles against the Syrian regime. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JULY 20: A member of Syrian Islamic Front carries bags inside the underground-tunnel that uses to explode military quarters of Syrian regime in Aleppo, Syria on July 20, 2014. As the Syrian civil-war continues, they mined a half-mile underground-tunnel, filled it with explosives during ongoing struggles against the Syrian regime. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JULY 19 : An injured kid is taken to hospital after Syrian forces bombed Aleppo's Etarib district, Syria leaving dozens of people injured, including kids on July 18, 2014. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JULY 16 : A Syrians man lays on the floor as others inspect the damaged building after Syrian regime army helicopters dropped several barrel bombs on opponent-controlled Muyesir region of Aleppo, Syria on July 16, 2014. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JULY 15: Wounded people are treated at the hospitals as a result of air attacks of Syrian army in Aleppo's Atarib district, Syria on July 15, 2014. (Photo by Ahmed Hasan Udeyb/Anadolu Agency/Getty Images)
Umm Mahmud sits next to her baby Mahmud Idilbi on July 12, 2014 in the Syrian city of Aleppo as a member of Syria Civil Defence has rescued him on June 18 from under the rubble of a building in the war-battered city. Mahmud Idlibi's dramatic rescue in the flashpoint northern city, a constant target of regime air raids, was shown in a video tweeted on July 11, 2014 by the team that saved him. AFP PHOTO/AMC/ZEIN AL-RIFAI (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)
Khaled (R), a member of Syria Civil Defence, kisses Syrian baby Mahmud Idilbi on July 12, 2014 in the Syrian city of Aleppo as Khaled has rescued the baby on June 18 from under the rubble of a building in the war-battered city. Mahmud Idlibi's dramatic rescue in the flashpoint northern city, a constant target of regime air raids, was shown in a video tweeted on July 11, 2014 by the team that saved him. AFP PHOTO/AMC/ZEIN AL-RIFAI (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)
ALEPPO, SYRIA - JULY 10: Syrian regime helicopters dropped barrel bombs to Al-Muyassar district of Aleppo that is under control of opposition activist in Aleppo on July 10, 2014. At least 20 people were killed during the operation of Syrian regime forces. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 30: June 30, 2014 dated pictures show many of the mosques in city of Aleppo of Syria lying in ruins as a result of the barrel bomb attacks organized by Assad forces. The Syrians in Aleppo having even more difficult days for Ramadan, the holy month of Muslims, since imams are not able to recite the azan due to the ongoing attacks. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 30: June 30, 2014 dated pictures show many of the mosques in city of Aleppo of Syria lying in ruins as a result of the barrel bomb attacks organized by Assad forces. The Syrians in Aleppo having even more difficult days for Ramadan, the holy month of Muslims, since imams are not able to recite the azan due to the ongoing attacks. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 30: June 30, 2014 dated pictures show many of the mosques in city of Aleppo of Syria lying in ruins as a result of the barrel bomb attacks organized by Assad forces. The Syrians in Aleppo having even more difficult days for Ramadan, the holy month of Muslims, since imams are not able to recite the azan due to the ongoing attacks. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 30: June 30, 2014 dated pictures show many of the mosques in city of Aleppo of Syria lying in ruins as a result of the barrel bomb attacks organized by Assad forces. The Syrians in Aleppo having even more difficult days for Ramadan, the holy month of Muslims, since imams are not able to recite the azan due to the ongoing attacks. (Photo by Halit Suleyman/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 25 : At least 15 people were killed and many houses were destroyed after Syrian regime helicopters dropped barrel bombs on the opposition controlled points of Aleppo on June 25, 2014. (Photo by Halit Suleyman/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 25 : At least 15 people were killed and many houses were destroyed after Syrian regime helicopters dropped barrel bombs on the opposition controlled Tariq al-Bab of Aleppo on June 25, 2014. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
MILAN, ITALY - JUNE 18: Two Syrian children show affection while waiting along with other Syrian refugees who arrived by train to the Milano Centrale railway station from southern Italy, accompanied by Italian police on June 18, 2014 in Milan, Italy. Syria's civil war has forced hundreds of refugees, including children to leave their homes with few possessions and head to the coasts of southern Italy, continuing on to Milan by train to be identified, processed, and apply for refugee status. (Photo by Pier Marco Tacca/Getty Images)
MILAN, ITALY - JUNE 18: Syrian children play games to occupy time while waiting along with other Syrian refugees who arrived by train to the Milano Centrale railway station from southern Italy, accompanied by Italian police on June 18, 2014 in Milan, Italy. Syria's civil war has forced hundreds of refugees, including children to leave their homes with few possessions and head to the coasts of southern Italy, continuing on to Milan by train to be identified, processed, and apply for refugee status. (Photo by Pier Marco Tacca/Getty Images)
MILAN, ITALY - JUNE 18: Syrian refugees arrive by train from southern Italy, accompanied by Italian police and wait in lines to be identified at the Milano Centrale railway station on June 18, 2014 in Milan, Italy. Syria's civil war has forced hundreds of refugees, including children to leave their homes with few possessions and head to the coasts of southern Italy, continuing on to Milan by train to be identified, processed, and apply for refugee status. (Photo by Pier Marco Tacca/Getty Images)
MILAN, ITALY - JUNE 18: Syrian refugees arrive by train to long lines at the Milano Centrale railway station from southern Italy, accompanied by Italian police on June 18, 2014 in Milan, Italy. Syria's civil war has forced hundreds of refugees, including children to leave their homes with few possessions and head to the coasts of southern Italy, continuing on to Milan by train to be identified, processed, and apply for refugee status. (Photo by Pier Marco Tacca/Getty Images)
MILAN, ITALY - JUNE 18: A Syrian baby drinks from a bottle while waiting along with other Syrian refugees who arrived by train to the Milano Centrale railway station from southern Italy, accompanied by Italian police on June 18, 2014 in Milan, Italy. Syria's civil war has forced hundreds of refugees, including children to leave their homes with few possessions and head to the coasts of southern Italy, continuing on to Milan by train to be identified, processed, and apply for refugee status. (Photo by Pier Marco Tacca/Getty Images)
ALEPPO, SYRIA, JUNE 16: Syrian regime helicopters dropped barrel bombs on the Sukkari neighbourhood, an opposition-held district in the northern Syrian city of Aleppo, on June 16, 2014, killing at least 36 people, including several children, according to the Syrian Observatory for Human Right. (Photo by Ahmed Muhammed Ali/Anadolu Agency/Getty Images)
ALEPPO, SYRIA, JUNE 16: Syrian regime helicopters dropped barrel bombs on the Sukkari neighbourhood, an opposition-held district in the northern Syrian city of Aleppo, on June 16, 2014, killing at least 36 people, including several children, according to the Syrian Observatory for Human Right. (Photo by Ahmed Muhammed Ali/Anadolu Agency/Getty Images)
ALEPPO, SYRIA, JUNE 16: Syrian regime helicopters dropped barrel bombs on the Sukkari neighbourhood, an opposition-held district in the northern Syrian city of Aleppo, on June 16, 2014, killing at least 36 people, including several children, according to the Syrian Observatory for Human Right. (Photo by Ahmed Muhammed Ali/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 14: Buildings are destroyed and fire starts after a barrel bomb attack in Aleppo, Syria on 14 June, 2014. 20 people killed and tens of people wounded as a result of barrel bomb attack of Syrian army's helicopters. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 13: Many people get wounded and many houses are demolished after a 'vacuum bomb' attack staged by Syrian regime forces' fighter jets in Mari town of Aleppo, Syria on June 13, 2014. People carry out search and rescue operation at the debris of the houses. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 13: Many people get wounded and many houses are demolished after a 'vacuum bomb' attack staged by Syrian regime forces' fighter jets in Mari town of Aleppo, Syria on June 13, 2014. People carry out search and rescue operation at the debris of the houses. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 7: Many houses are demolished and damaged in an air attack staged by Syrian regime's air forces to Hayyan town of Aleppo, Syria on June 7, 2014. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 4: Military troops of Syrian Islamic Front attack military quarters which belongs to Syrian regime in south of Aleppo, Syria on June 4, 2014. (Photo by Ahmed Hasan Ubeyd/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 02 : At least 15 people including children were killed and many injured after Syrian regime forces have launched an air attack in Aleppo, Syria on June 2, 2014. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 02 : At least 15 people including children were killed and many injured after Syrian regime forces have launched an air attack in Aleppo, Syria on June 2, 2014. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 02 : At least 15 people including children were killed and many injured after Syrian regime forces have launched an air attack in Aleppo, Syria on June 2, 2014. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 3: Apartments are destroyed on the attack of Syrian army with heavy weapons in Aleppo, Syria on 3 June, 2014. It is informed that 100 people (13 children, 7 women) died on the attack. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - JUNE 02 : At least 15 people including children were killed and many injured after Syrian regime forces have launched an air attack in Aleppo, Syria on June 2, 2014. (Photo by Salih Mahmud Leyla/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - MAY 28 : Many people died and many houses demolished after Syrian regime forces have launched an air attack in the town of Mari, Aleppo on May 28, 2014. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
A fireman sprays water on Syrian expatriates living in Lebanon to keep them cool, as they arrive to cast their ballots in their country's presidential elections, outside the Syrian Embassy in Yarze east of Beirut on May 28, 2014. Filling the streets around the embassy in Beirut, thousands of Syrians turned out to vote in a controversial presidential election that Bashar al-Assad is expected to clinch effortlessly, as civil war rages. AFP PHOTO/ JOSEPH EID (Photo credit should read JOSEPH EID/AFP/Getty Images)
A Syrian living in Jordan takes part in a protest against the Syrian presidential elections, near the Syrian embassy in Amman on May 28, 2014. Polls open in Syrian embassies for refugees who fled their homeland through recognised checkpoints, in a controversial election expected to return President Bashar al-Assad to office despite three years of civil war. AFP PHOTO/ KHALIL MAZRAAWI (Photo credit should read KHALIL MAZRAAWI/AFP/Getty Images)
A fireman sprays water on Syrian expatriates living in Lebanon to keep them cool, as they arrive to cast their ballots in their country's presidential elections, outside the Syrian Embassy in Yarze east of Beirut on May 28, 2014. Filling the streets around the embassy in Beirut, thousands of Syrians turned out to vote in a controversial presidential election that Bashar al-Assad is expected to clinch effortlessly, as civil war rages. AFP PHOTO/ JOSEPH EID (Photo credit should read JOSEPH EID/AFP/Getty Images)
Rescue teams carry victims pulled out from the rubble of a destroyed building following a barrel bomb strike said to be launched by Syrian government forces on May 26, 2014 in the northern Syrian city of Aleppo in which serveral people were reported killed or wounded. Syrian President Bashar al-Assad, facing two little-known challengers in a June 3 presidential election, is widely expected to clinch a third seven-year term despite Syria's civil war, which has killed more than 160,000 people. AFP PHOTO / BARAA AL-HALABI (Photo credit should read BARAA AL-HALABI/AFP/Getty Images)
Syrian men search the rubble for survivors in a destroyed building following reported barrel bomb strikes by Syrian government forces on May 26, 2014 in the northern Syrian city of Aleppo. Syrian President Bashar al-Assad, facing two little-known challengers in a June 3 presidential election, is widely expected to clinch a third seven-year term despite Syria's civil war, which has killed more than 160,000 people. AFP PHOTO / BARAA AL-HALABI (Photo credit should read BARAA AL-HALABI/AFP/Getty Images)
ALEPPO, SYRIA - MAY 4: Islamic Front forces staged a Grad rocket attack in Breyc village, under the control of Syrian regime, Aleppo on May 4, 2013. (Photo by Ahmed Hasan Ubeyd/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - MAY 4: Islamic Front forces staged a Grad rocket attack in Breyc village, under the control of Syrian regime, Aleppo on May 4, 2013. (Photo by Ahmed Hasan Ubeyd/Anadolu Agency/Getty Images)
Wounded people receive medical care at a makeshift hospital following a reported bombardment with explosive-packed 'barrel bombs' by Syrian government forces on May 4, 2014 in the al-Sakhour district of the northern city of Aleppo. The June 3 election in Syria is being held amid a brutal civil war that has killed more than 150,000 people since March 2011 and made millions homeless. AFP PHOTO / AMC / ZEIN AL RIFAI (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)
ALEPPO, SYRIA - MAY 3: At least 53 people including women and children were killed on Saturday in rebel-held areas of Syria, which were hit by regime artillery and airstrikes in Aleppo on May 3, 2014. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
ALEPPO, SYRIA - MAY 3: At least 53 people including women and children were killed on Saturday in rebel-held areas of Syria, which were hit by regime artillery and airstrikes in Aleppo on May 3, 2014. (Photo by Mamun Ebu Omer/Anadolu Agency/Getty Images)
HATAY, TURKEY - APRIL 28: 2 of the 34 Syrians wounded during the clashes in Kasab town of Latakia, near turkish border, who were brought to Turkish city of Hatay has lost their lives, April 28, 2014. (Photo by Halit Demir/Anadolu Agency/Getty Images)
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The Britain-based Observatory said that was the single largest daily death toll since the U.S.-backed Syria Democratic Forces (SDF), a group of Kurdish and Arab militias, began their assault on Raqqa last June after a long campaign to isolate Islamic State inside the city.

Former Raqqa residents in touch with relatives still in the city echoed this view to Reuters.

The U.S.-led coalition says it is careful to avoid civilian casualties in its bombing runs against Islamic State in both Syria and Iraq, and investigates any allegations.

"The Coalition respects human life and is assisting partner forces in their effort to liberate their land from ISIS while safeguarding civilians. Our goal is always for zero civilian casualties," a statement sent to Reuters by the Pentagon said

The Observatory said bombs that hit the al-Sakhani and Harat al-Bado districts on Monday were close to a multi-story residential building that had been bombed the day before, killing at least 27 civilians, including seven children.

Former Raqqa residents in touch with relatives gave a higher death toll, saying many bodies were still under rubble.

The SDF alliance, spearheaded by the Kurdish YPG militia, has been waging fierce battles inside the Old City area of Raqqa since last month. Fighting is now intensifying near the city center as the U.S.-backed forces close in on Islamic State.

Footage of the Old City released by activists showed extensive damage to buildings around the historic Old Mosque.

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US led airstrikes on ISIS targets
Smoke rises after an U.S.-led air strike in the Syrian town of Kobani Ocotber 8, 2014. U.S.-led air strikes on Wednesday pushed Islamic State fighters back to the edges of the Syrian Kurdish border town of Kobani, which they had appeared set to seize after a three-week assault, local officials said. The town has become the focus of international attention since the Islamists' advance drove 180,000 of the area's mostly Kurdish inhabitants to flee into adjoining Turkey, which has infuriated its own restive Kurdish minority-- and its NATO partners in Washington -- by refusing to intervene. REUTERS/Umit Bektas (SYRIA - Tags: POLITICS CONFLICT TPX IMAGES OF THE DAY)
Pictures showing an ISIL Command and Control Center in Syria before (L) and after it was struck by bombs dropped by a U.S. F-22 fighter jet are seen in handouts released by the U.S. Department of Defense (DOD) September 23, 2014. This was the first time the F22 was used in a combat role according to the DOD. The United States and its Arab allies bombed Syria for the first time on Tuesday, killing scores of Islamic State fighters and members of a separate al Qaeda-linked group, opening a new front against militants by joining Syria's three-year-old civil war. REUTERS/US Department of Defense/Handout (UNITED STATES - Tags: MILITARY CONFLICT) THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS
In this photograph taken on April 11, 2017, smoke rises after an air strike by US aircraft on positions during an ongoing an operation against Islamic State (IS) militants in the Achin district of Afghanistan's Nangarhar province. An American special forces soldier has been killed while conducting operations against the Islamic State group in Afghanistan, the US military said.�The US-backed Afghan military has vowed to wipe out the group in its strongholds in the eastern province of Nangarhar as IS challenges the more powerful Taliban on its own turf. / AFP PHOTO / NOORULLAH SHIRZADA (Photo credit should read NOORULLAH SHIRZADA/AFP/Getty Images)
A still image captured from U.S. Navy video footage shows a Tomahawk Land-Attack Missile (TLAM) is launched against ISIL targets from the guided-missile cruiser USS Philippine Sea in the Gulf, September 23, 2014. The United States and Arab allies hit Islamic State (IS) targets including training camps, headquarters and weapon supplies in northern and eastern Syria in dozens of air and missile strikes on Tuesday, the U.S. military and a monitoring group said. REUTERS/Abe McNatt/U.S. Navy/Handout (MID-SEA - Tags: MILITARY CIVIL UNREST POLITICS) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS
Smoke rises after an air strike on Islamic State (IS) militants positions during an ongoing operation against the group in the Achin district of Afghanistan's Nangarhar province on April 14, 2017, a day after the US military struck the district with its largest non-nuclear bomb. The US military's largest non-nuclear bomb killed dozens of Islamic State militants as it smashed their mountain hideouts, Afghan officials said April 14, ruling out any civilian casualties despite the weapon's destructive capacity. The GBU-43/B Massive Ordnance Air Blast bomb -- dubbed the 'Mother Of All Bombs' -- hit IS positions in Achin district in eastern Nangarhar province on April 13. / AFP PHOTO / NOORULLAH SHIRZADA (Photo credit should read NOORULLAH SHIRZADA/AFP/Getty Images)
MOSUL, IRAQ - NOVEMBER 7: Smoke rises from Daesh terrorists positions after U.S.-led coalition's airstrike over east of Bashiqa town in Mosul, Iraq on November 7, 2016. Iraqi Kurdish Regional Government's peshmerga forces entered Bashiqa Town center as the operation to retake Iraq's Mosul from Daesh terrorists continues, in Mosul. A much anticipated Mosul offensive to liberate the city from Daesh began midnight of 16th of October 2016. (Photo by Hemn Baban/Anadolu Agency/Getty Images)
Photo taken on 30 January 2017 in Mosul, Iraq. Destroyed hospital. Saalam hospital was targeted by a U.S. Coalition airstrike in December, 2016 as it was a base for Islamic State commanders. 16th Division command and control the east side of the city. The soldiers are engaged in the search for militants ISIS. The army protects the eastern bank of the Tigris. Soldiers take up positions on the roofs of buildings of which observe areas next to the river. (Photo by Maciej Moskwa/NurPhoto via Getty Images)
MOSUL, IRAQ - NOVEMBER 7: Smoke rises from Daesh terrorists positions after U.S.-led coalition's airstrike over east of Bashiqa town in Mosul, Iraq on November 7, 2016. Iraqi Kurdish Regional Government's peshmerga forces entered Bashiqa Town center as the operation to retake Iraq's Mosul from Daesh terrorists continues, in Mosul. A much anticipated Mosul offensive to liberate the city from Daesh began midnight of 16th of October 2016. (Photo by Yunus Keles/Anadolu Agency/Getty Images)
Members of Iraq's elite counter-terrorism service patrol as smoke billows in the background following a reported air strike by the US-led coalition on December 29, 2015 on the outskirts of Ramadi, the capital of Iraq's Anbar province, about 110 kilometers west of Baghdad, after Iraqi forces recaptured it from the Islamic State (IS) jihadist group. Iraq declared the city of Ramadi liberated from the Islamic State group Monday and raised the national flag over its government complex after clinching a landmark victory against the jihadists. AFP PHOTO / AHMAD AL-RUBAYE / AFP / AHMAD AL-RUBAYE (Photo credit should read AHMAD AL-RUBAYE/AFP/Getty Images)
ALEPPO, SYRIA - DECEMBER 03: Smoke rises after the US-led coalition airstrikes' hits DAESH positions at Brekida village in Aleppo, Syria on December 03, 2015. (Photo by Huseyin Nasir/Anadolu Agency/Getty Images)
Kurdish Peshmerga soldiers on November 14, 2015 in Sinjar, Iraq. Kurdish forces, with the aid of months of U.S.-led coalition airstrikes, liberated the town from ISIL extremists, known in Arabic as Daesh, in recent days. Although the battle was deemed a major victory, much of the city lay in complete ruins. (Photo by Andrea DiCenzo/NurPhoto) (Photo by Andrea DiCenzo/NurPhoto/NurPhoto via Getty Images)
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Amaq, an Islamic State-affiliated news agency, released a video on Monday showing at least a dozen corpses, many of them children, lying on the floor. It claimed the video was shot in Raqqa on Monday and showed victims of coalition air strikes, as well as extensive damage to residential areas.

Reuters could not verify the authenticity of the video.

An activist-run group "Raqqa is Being Slaughtered Silently" said it had documented at least 946 civilian deaths since the Raqqa offensive began in June.

The United Nations says at least 200,000 people have fled Raqqa in recent months and that up to 20,000 civilians remain trapped inside.

The plight of civilians left in the city has worsened, with water cut off for over two months and shortages of food, leaving many of those remaining living on canned foods. (Reporting by Suleiman Al-Khalidi, editing by Larry King)

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