Russia’s defense ministry on Friday said it believes it has killed the leader of ISIS, according to multiple reports, though it added information on the death is still “being verified.”

Islamic State leader Abu Bakr al-Baghdadi was killed in an airstrike late last month, Moscow said, in what would be a devastating blow for the terror group as it clings to its remaining enclaves in Iraq and Syria.

A spokesman for the U.S.-led coalition against ISIS told the Associated Press he could not confirm the death.

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Previous reports of Baghdadi’s death have turned out to be false, and Russian Foreign Minister Sergey Lavrov said he didn’t “have a 100 percent confirmation of the information.”

The BBC reported the strike on May 28 may have killed as many as 330 other militants.

The news comes as ISIS is besieged in its two largest remaining strongholds: its de facto capital Raqqa in Syria, where the Russian strike occurred, and Mosul in Iraq.

It’s not immediately clear who would replace Baghdadi as ISIS leader.