A group that monitors the war in Syria said on Tuesday it has "confirmed information" about the death of Abu Bakr al-Baghdadi, the leader of Islamic State, citing information received from the militants in eastern Syria.
The Britain-based Syrian Observatory for Human Rights said it had information that confirmed the death of the IS leader.
"We learned of it today but we do not know when he died or how," director Rami Abdel Rahman said.
Baghdadi's death has been rumoured numerous times in the past, and it was not immediately possible to independently verify the claim. There also were no immediate announcements from Islamic State's news channels.
The US Central Command said in a statement, "We cannot confirm this report, but hope it is true."
Tongue in cheek, the statement added, "We strongly advise ISIS to implement a strong line of succession. It will be needed."
In Baghdad, the commander of coalition forces in Iraq said he hoped Baghdadi was "deader than a doornail", but he cautioned that regardless of whether the terror leader was alive or dead, the fight to reclaim all of Iraq from the group's grip was far from over.
"I don't have a clue," Lieutenant General Stephen Townsend told Pentagon reporters when asked about Baghdadi's fate during a briefing from Baghdad. "Don't have a reason to believe he's alive. Don't have a reason to believe he's dead."
Townsend added, "If he is dead, that means someone's running ISIS and I think that they're trying to keep his death quiet for their own morale."
There has been a steady stream of reports regarding Baghdadi's death in recent weeks, including claims to this effect by the Russians, the Syrians and the Iranians.
The death of Baghdadi - if true - would mark another blow to the extremist group days after it was finally driven from the northern Iraqi city of Mosul by Iraqi-led forces. The militants are also under siege in the Syrian city of Raqqa, the Islamic State's self-declared capital, where a US-backed force of mainly Kurdish fighters has been advancing for weeks.
The Syrian Observatory for Human Rights relies on a network of activists in Syria for its reporting. The group's director, who goes by the pseudonym Rami Abdulrahman (or Abdel Rahman) said Islamic State leaders had confirmed Baghdadi's death to the Observatory's activists in the Syrian province of Deir al-Zour.
A post on the Syrian Observatory's website said it "confirmed information … about the death" of Baghdadi, whose real name is Ibrahim Awad Ibrahim al-Badry.
Baghdadi's breakaway al-Qaida faction gradually formed into the core of the Islamic State. But the various earlier reports about his death proved false or could not be substantiated.
Last month, Russia said it was looking into claims that one of its airstrikes in late May outside Raqqa killed Baghdadi. The Russian military later said it could find no clear evidence of Baghdadi's death. The US military also said at the time it had "no information to corroborate" the Russia reports.
As far back as December 2012, Iraqi officials claimed that they had captured Baghdadi in Baghdad. Iraqi commanders later said the person held was not Baghdadi.