Exclusive: Watchdog to probe alleged mustard gas use by Islamic state

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Islamic State Destroys Part of Ancient Syrian Temple

THE HAGUE (Reuters) -- Islamic State militants "most probably" used the banned chemical weapon mustard gas against Kurdish forces in Iraq and international inspectors have been asked to investigate, diplomatic sources told Reuters.

A team of inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) will go to Iraq next week to help determine if the blistering agent sulfur mustard was used in the battlefield, three sources told Reuters.

Islamic State already has a broad arsenal of weapons and military vehicles seized from Iraqi forces. It launched an attack with "weaponized chlorine" in January and there have been at least four other occasions it allegedly used chemical weapons, regional officials said.

If Islamic State insurgents have obtained sulfur mustard, commonly known as mustard gas, it would signal a dangerous development in a conflict that has already destabilized the region.

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Exclusive: Watchdog to probe alleged mustard gas use by Islamic state
FILE - In this Monday, April 19, 2010 file photo, Iraq's Prime Minister Nouri al-Maliki holds a paper displaying photographs of a man the Iraqi government claims to be al-Qaida leader Abu Omar al-Baghdadi at a news conference in Baghdad, Iraq. U.S. and Iraqi forces killed the two top al-Qaida in Iraq leaders on April 18, 2010, allowing Abu Bakr al-Baghdadi to become the leader of a terror group weakened by a concerted campaign aimed at ending a Sunni insurgency in the country.(AP Photo/Hadi Mizban, File)
FILE - In this Feb. 21, 2009 file photo, guards stand at the entrance of a renovated Abu Ghraib prison, now renamed Baghdad Central Prison and run by Iraqis, in Baghdad, Iraq. A military-style assault by al-Qaida leader Abu Bakr al-Baghdadi’s fighters on two Baghdad-area prisons in July, 2013 freed more than 500 inmates.(AP Photo / Karim Kadim, File)
FILE - In this Wednesday April 21, 2010 file photo, an Iraqi military helicopter flies over the site of a joint U.S.-Iraqi raid that reportedly killed Abu Omar al-Baghdadi and Abu Ayyub al-Masri, two top-ranking al-Qaida figures, about six miles (10 kilometers) southwest of Tikrit. U.S. and Iraqi forces killed the two top al-Qaida in Iraq leaders on April 18, 2010, allowing Abu Bakr al-Baghdadi to become the leader of a terror group weakened by a concerted campaign aimed at ending a Sunni insurgency in the country.(AP Photo/Karim Kadim, File)
FILE - In this Dec. 10, 2010 photo, pictures of slain Iraqi Christians are displayed during Mass at Our Lady of Salvation church in Baghdad, Iraq. Abu Bakr al-Baghdadi’s al-Qaida militants attacked the church on Oct. 31 during Sunday night mass, killing 58 people in the deadliest assault targeting Christians since the 2003 U.S.-led invasion there. The militants reportedly demand the release of Muslim women they claim were held by Egypt’s Coptic Christian church.(AP Photo/Hadi Mizban, File)
FILE - In this Wednesday, Aug. 1, 2012 file photo, Iraqis inspect the aftermath a day after a car bomb attack in a shopping area in Karradah, Baghdad, Iraq. In his first purported online message on July 21, 2012, al-Qaida in Iraq leader Abu Bakr al-Baghdadi promised to regain lost ground in Iraq and calls on militants to “chase and liquidate the judges, the investigators and the guards.” Within days, his group begins a campaign of attacks, car bombings and other assaults killing hundreds.(AP Photo/Khalid Mohammed, File)
FILE - In this April 23, 2013 file photo, a suspected Yemeni al-Qaida militant, center, holds a banner as he stands behind bars during a court hearing in state security court in Sanaa, Yemen. In a competition with the Islamic State group for recruits and prestige across the Middle East, al-Qaida has sought to distinguish itself from its rival's bloodthirstiness, taking an approach that in jihadi circles would be considered pragmatic. (AP Photo/Hani Mohammed, File)
A sign on the northern road exiting the town of Gao, Northern Mali, Wednesday Jan. 30, 2013, reads "welcome to the islamic state of Gao". Islamist extremists fled the city Saturday after French, Chadian and Nigerien troops arrived, ending 10 months of radical islamic control over the city.(AP Photo/Jerome Delay)
FILE - In this Sunday, March 30, 2014, file photo, Islamic State group militants hold up their flag as they patrol in a commandeered Iraqi military vehicle in Fallujah, 40 miles (65 kilometers) west of Baghdad, Iraq. Abu Bakr al-Baghdadi’s forces swept into Ramadi and Fallujah in Iraq’s Anbar province, which Iraqi security forces had abandoned weeks earlier. That came after security forces killed demonstrators during a Sunni protest, effectively turning the unrest into an uprising.(AP Photo, File)
FILE - In this June 23, 2014, file photo, fighters from the Islamic State group parade in a commandeered Iraqi security forces armored vehicle down a main road at the northern city of Mosul, Iraq. Abu Bakr Al-Baghdadi’s fighters took over Iraq's second-largest city of Mosul in June, 2014, followed by Saddam Hussein's hometown of Tikrit and smaller communities in the Sunni heartland as government forces melt away.(AP Photo/File)
German Kreshnik B. waits for the beginning of his trial at a higher regional court in Frankfurt, Germany, Monday, Sept.15, 2014. He is accused of having been a member of the Islamic state group in Syria. He was arrested when he came back to Germany in December 2013. (AP Photo/Michael Probst)
FILE - In this Monday, June 16, 2014 file photo, demonstrators chant pro-Islamic State group slogans as they wave the group's flags in front of the provincial government headquarters in Mosul, 225 miles (360 kilometers) northwest of Baghdad, Iraq. The IS declaration of a "caliphate" in Iraq and Syria inspired a stream of thousands of foreign fighters to join it and earned it pledges of allegiance by individual militants around the region. (AP Photo, File)
FILE - In this Monday, Nov. 24, 2014, file photo, smoke billows behind an Islamic State group sign during clashes between militants from the Islamic State group and Iraqi security forces during a military operation to regain control of the town of Sadiyah, 60 miles (95 kilometers) north of Baghdad, Iraq in Diyala province, Iraq. In a competition with the Islamic State group for recruits and prestige across the Middle East, al-Qaida has sought to distinguish itself from its rival's bloodthirstiness, taking an approach that in jihadi circles would be considered pragmatic. (AP Photo, File)
A photograph on a television screen shown by Army Lt. Gen. William Mayville, Jr., Director of Operations J3, while he briefs the news media on operations in Syria, at the Pentagon in Arlington, Va., Tuesday, Sept. 23, 2014. (AP Photo/Cliff Owen)
This image provided by the Department of Defense shows a image that was shown by Army Lt. Gen. William Mayville, Jr., Director of Operations J3, during a briefing on operations in Syria, at the Pentagon in Washington on Tuesday, Sept. 23, 2014. (AP Photo/Department of Defense)
This image provided by the Department of Defense shows a image that was shown by Army Lt. Gen. William Mayville, Jr., Director of Operations J3, during a briefing on operations in Syria, at the Pentagon in Washington on Tuesday, Sept. 23, 2014. (AP Photo/Department of Defense)
FILE - In this Monday, Nov. 24, 2014 file photo, Iraqi army soldiers deploy in front of a court run by the Islamic State group after a military operation to regain control of the town of Sadiyah in Diyala province, 60 miles (95 kilometers) north of Baghdad, Iraq. (AP Photo, File)
Iraqi security forces prepare to attack Islamic State extremist positions in central Tikrit, 130 kilometers (80 miles) north of Baghdad, Iraq, Sunday, March 29, 2015. (AP Photo/Khalid Mohammed)
Black flags used by the Islamic State group are seen over their combat positions in the Rashad Bridge, which connects the provinces of Salah al-Din and Kirkuk, 290 kilometers (180 miles) north of Baghdad, Iraq, Monday, Sept. 29, 2014. (AP Photo/Hadi Mizban)
Syrian Kurdish fighter Delkhwaz Sheikh Ahmad, 22, checks a picture on his mobile showing Islamic State group fighters killed in fighting with Syrian Kurdish fighters, as he prepares to leave for Kobani, Syria, to rejoin the fighting, at his brother's house in Suruc, on the Turkey-Syria border, Friday, Oct. 17, 2014. The father of two is a member of the People’s Protection Units, also known as YPG and is fighting against militants of the Islamic State group in Kobani, Syria. Every few weeks, he takes a couple of days to cross the border into Turkey to visit his family that had evacuated. Kobani, also known as Ayn Arab, and its surrounding areas, has been under assault by extremists of the Islamic State group since mid-September and is being defended by Kurdish fighters. (AP Photo/Lefteris Pitarakis)
FILE - In this Aug. 10, 2014 file photo, an aircraft lands after missions targeting the Islamic State group in Iraq from the deck of the U.S. Navy aircraft carrier USS George H.W. Bush in the Persian Gulf. Combined U.S.-Arab airstrikes at the heart of the Islamic State group's military strongholds in Syria achieved their strategic aim of showing the extremists that their savage attacks will not go unanswered, the top American military officer said Tuesday, Sept. 23, 2014. (AP Photo/Hasan Jamali, File)
In this image made from video broadcast on Egyptian state television on Monday, Feb. 16, 2015, a fighter jet leaves the hangar in preparation to launch airstrikes against Islamic State targets in Libya after the extremist group released a grisly video showing the beheading of several Egyptian Coptic Christians it had held hostage for weeks. (AP Photo/Egyptian State Television via AP video)
In this image released by the Egyptian Presidency in the early hours of Monday, Feb. 16, 2015, President Abdel-Fattah el-Sissi makes a statement after militants in Libya affiliated with the Islamic State group released a grisly video showing the beheading of several Egyptian Coptic Christians it had held hostage for weeks. Egypt said Monday it has launched airstrikes against Islamic State targets in Libya following the release of the video, marking the first time Cairo has publicly acknowledged taking military action in neighboring Libya, where extremist groups seen as a threat to both countries have taken root in recent years. (AP Photo/Egyptian Presidency)
A man is comforted by others as he mourns over Egyptian Coptic Christians who were captured in Libya and killed by militants affiliated with the Islamic State group, outside of the Virgin Mary church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo, Egypt, Monday, Feb. 16, 2015. Egyptian warplanes struck Islamic State targets in Libya on Monday in swift retribution for the extremists' beheading of a group of Egyptian Christian hostages on a beach, shown in a grisly online video released hours earlier. (AP Photo/Hassan Ammar)
Iraqi security forces participate in a drill as U.S. forces train them in Taji, north of Baghdad, Iraq, Saturday, March 21, 2015. U.S. military officials have said a coordinated military mission to retake Mosul, Iraq's second largest city held by the Islamic State group, will likely begin in April or May and involve up to 25,000 Iraqi troops. But the Americans have cautioned that if the Iraqis are not ready, the offensive could be delayed. Iraqi officials have backed away from setting a timeline. (AP Photo/Karim Kadim)
Iraqi security forces participate in a drill as U.S. forces help train them in Taji, north of Baghdad, Iraq, Saturday, March 21, 2015. U.S. military officials have said a coordinated military mission to retake Mosul, Iraq's second largest city held by the Islamic State group, will likely begin in April or May and involve up to 25,000 Iraqi troops. But the Americans have cautioned that if the Iraqis are not ready, the offensive could be delayed. Iraqi officials have backed away from setting a timeline. (AP Photo/Karim Kadim)
A bombs, seen top left, falls on an Islamic State position in eastern Kobani, during an airstrike by the US led coalition, seen from a hilltop outside Suruc, on the Turkey-Syria border Saturday, Nov. 8, 2014. Kobani, also known as Ayn Arab, and its surrounding areas, has been under assault by extremists of the Islamic State group since mid-September and is being defended by Kurdish fighters. (AP Photo/Vadim Ghirda)
This picture released late Thursday, Aug. 20, 2015, by an Islamic State militant-affiliated website, shows a bulldozer, background, of the Islamic State militants destroying the Saint Eliane Monastery near the town of Qaryatain which IS captured in early August, in Homs province, Syria. A priest and activists say the Islamic State group has demolished an ancient monastery in central Syria. A Christian clergyman told The Associated Press in Damascus that IS militants also wrecked a church inside the monastery that dates back to the first Christian centuries. The priest, who spoke Friday on condition of anonymity for fear of reprisals, said the monastery included an Assyrian Catholic church. (Islamic State militant website via AP)
Mourners carry the coffins of victims of Saturday's Ankara bombing attacks, during a funeral in Istanbul, Monday, Oct. 12, 2015. Turkish investigators are close to identifying one of the suicide bombers in Turkey's deadliest attacks in years, Prime Minister Ahmet Davutoglu said Monday, adding that the Islamic State group was the "Number one priority" of the investigation. (AP Photo/Lefteris Pitarakis)
Armoured police vehicles patrol as they block a road leading to the site of armed clashes with militants in Diyarbakir, southeastern Turkey, Monday, Oct. 26, 2015. Police raided a house used by a suspected cell of the Islamic State group triggering a clash that killed up to seven militants and two policemen, Turkish media reports said. It was not immediately clear if the operation was linked to suicide bombings of a peace rally in the capital Ankara earlier this month that killed 102 people. (AP Photo/Mahmut Bozarslan)
From left, German Chancellor Angela Merkel, French president Francois Hollande and Paris Mayor Anne Hidalgo hold a white rose as they pay their respects to the victims of the attacks of the 13th November on the Place de la Republique prior to a meeting at the Elysee Palace, in Paris, Wednesday, Nov. 25, 2015. Merkel's visit to Paris is part of president Hollande's diplomatic offensive to get the international community to bolster the campaign against the Islamic State militants. (Etienne Laurent, Pool Photo via AP)
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Sulfur mustard is a Class 1 chemical agent, which means it has few uses outside chemical warfare. A blistering agent that causes severe delayed burns to the eyes, skin and respiratory tract, it was used on a massive scale during World War One.

Kurdish authorities say 35 troops southwest of the regional capital of Erbil were sickened in August by a chemical attack. Blood samples tested positive for mustard gas, they said earlier this month.

"Most probably it was mustard gas," said one diplomat, who spoke on condition of anonymity because the information was classified, "But we want to make sure and we want to know where it came from because it is very difficult to get."

Chemical agents are not believed to have been used in fighting in Iraq since Saddam Hussein's fall in 2003.

If confirmed by the OPCW, it would raise serious questions about how Islamic State militants got their hands on the chemicals and, crucially, where they came from.

There are no declared stockpiles of mustard gas in the Middle East since Syria joined the Chemical Weapons Convention in 2013, vowing to eliminate its chemical weapons program.

The OPCW team's mandate will be limited to the single allegation of use in August against the Kurdish Peshmerga forces, which was allegedly fired using mortar rounds.

Syria declared 1,300 tonnes of chemicals weapons to the OPCW in 2013 as part of a deal with Russia, avoiding air strikes that had been threatened by the United States.

Amid continued allegations of the use of prohibited chlorine barrel bombs in Syria, Damascus is in discussions with the OPCW about whether it accurately and fully disclosed its chemical weapons program.

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