The Syrian Observatory for Human Rights war monitor said today it had information from top Islamic State group leaders confirming the death of the jihadist organisation's chief Abu Bakr al-Baghdadi.
"Top tier commanders from IS who are present in Deir Ezzor province have confirmed the death of Abu Bakr al- Baghdadi, emir of the Islamic State group, to the Observatory," director Rami Abdel Rahman told AFP.
"We learned of it today but we do not know when he died or how."
Deir Ezzor, in eastern Syria, remains largely under IS control even as the group is losing territory elsewhere in the country and in neighbouring Iraq.
Abdel Rahman said Baghdadi "was present in eastern parts of Deir Ezzor province" in recent months, but it was unclear if he was killed in the area or elsewhere.
There have been persistent rumours of Baghdadi's death in recent months, and Russia's military said in mid-June that it was seeking to verify whether it had killed the IS chief in an air strike in Syria in May.
Russia's army said Sukhoi warplanes carried out a 10- minute raid on May 28 at a location near the IS stronghold of Raqa, where group leaders had gathered to plan a pullout from the area.
The US-led coalition fighting the jihadist group in Syria and Iraq said at the time it could not confirm whether the Russian strike had killed Baghdadi.
The 46-year-old Iraqi-born leader of IS has not been seen in public since making his only known public appearance as "caliph" in 2014 at the Grand Mosque of Al-Nuri in Mosul.
IS destroyed the highly symbolic site before Iraqi forces could reach it as they pushed the jihadist group from Mosul, where Iraq's government formally declared victory on Monday.
With a USD 25-million US bounty on his head, Baghdadi has kept a low profile and was rumoured to move regularly throughout IS-held territory in the area straddling Iraq and Syria.
His death, if confirmed, would be a new blow to the group which is also battling a US-backed coalition of Kurdish and Arab fighters for control of its Syrian stronghold Raqa.