The Syrian Observatory for Human Rights told Reuters on Tuesday it had "confirmed information" that Islamic State leader Abu Bakr al-Baghdadi had been killed.
The report came just days after the Iraqi army recaptured the last sectors of the northern Iraqi city of Mosul, which Baghdadi's forces overran almost exactly three years ago.
Russia's Defence Ministry said in June that it might have killed Baghdadi when one of its air strikes hit a gathering of Islamic State commanders on the outskirts of the Syrian city of Raqqa. Washington said it could not corroborate the death and Western and Iraqi officials have been skeptical.
Click through images of U.S. led airstrikes on ISIS targets:
US led airstrikes on ISIS targets
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.ï¿½The 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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Reuters could not independently verify Baghdadi's death.
"(We have) confirmed information from leaders, including one of the first rank who is Syrian, in the Islamic State in the eastern countryside of Deir al-Zor," said Rami Abdulrahman, the director of the Britain-based war monitoring group.
In Iraq, U.S. Army Colonel Ryan Dillon, spokesman for the U.S.-led coalition fighting Islamic State, said he could not confirm the news.
The top U.S. general in Iraq later said the coalition had no concrete information.
"Despite all the helpful reports to us from every source imaginable, I'm unable to confirm or deny either where he is, or whether he is alive or dead. Let me just say for the record, my fervent hope is it is the latter," Lieutenant General Stephen Townsend told a news briefing.
Abdulrahman said activists working with him in Deir al-Zor had been told by the Islamic State sources that Baghdadi had died, but not when or how. The sources said Baghdadi had been present in the eastern countryside of Syria's Deir al-Zor province in the past three months.
The Pentagon said it had no information to corroborate the reports. Kurdish and Iraqi officials also had no immediate confirmation.
Baghdadi's death has been announced many times before, but the Observatory has a record of credible reporting on the Syrian conflict. Islamic State-affiliated websites and social media feeds have so far said nothing.
The death of Baghdadi, who declared a caliphate governed by Islamic law from a mosque in Mosul in 2014, would be one of the biggest blows yet to the jihadist group, which is trying to defend shrinking territory in Syria and Iraq.
The United States put up a $25 million reward for his capture, the same amount as it had offered for al Qaeda leader Osama bin Laden and his successor Ayman al-Zawahri. It is not yet known if anybody will claim the bounty.
The Islamic State leaders killed in Iraq and Syria since the U.S.-led coalition began its air strikes include Abu Ali al-Anbari, Baghdadi's deputy; the group's "minister of war," Abu Omar al-Shishani, a close military adviser to Baghdadi; and Abu Mohammad al-Adnani, one of its most prominent and longest-serving leaders.
FAMILY OF PREACHERS
Baghdadi was born Ibrahim Awad al-Samarrai in 1971 in Tobchi, a poor area near Samarra, north of the capital Baghdad.
His family included preachers from the ultra-conservative Salafi school of Sunni Islam, which sees many other branches of the faith as heretical and other religions as anathema.
He joined the Salafi jihadist insurgency in 2003, the year of the U.S.-led invasion of Iraq, and was captured by the Americans. They released him about a year later, thinking he was a civilian agitator rather than a military threat.
It was not until July 4, 2014, that he seized the world's attention, climbing the pulpit of Mosul's medieval al-Nuri mosque in black clerical garb during Friday prayers to announce the restoration of the caliphate.
Thousands of volunteers flocked into Iraq and Syria from around the world to become "Jund al-Khilafa," or soldiers of the caliphate.
At the height of its power two years ago, Islamic State ruled over millions of people in territory running from northern Syria through towns and villages along the Tigris and Euphrates river valleys to the outskirts of the Iraqi capital Baghdad.
It claimed or inspired attacks in dozens of cities including Paris, Nice, Orlando, Manchester, London and Berlin, and in nearby Turkey, Iran, Saudi Arabia and Egypt.
In Iraq, it staged dozens of attacks targeting Shi'ite Muslim areas. A truck bomb in July 2016 killed more than 324 people in a crowded area of Baghdad, the deadliest attack since the 2003 invasion of Iraq.
The loss of Mosul and the siege of Raqqa, Islamic State's capital in Syria, by a U.S.-backed, Kurdish-led force stripped Baghdadi of the trappings of caliph and made him a fugitive in the desert border area between the two countries.
(Additional reporting by Suleiman al-Khalidi in Beirut, Omar Fahmy in Cairo and Phil Stewart in Washington; Writing by Ahmed Aboulenein and Samia Nakhoul; Editing by Kevin Liffey)