Moscow claims an air strike may have killed Abu Bakr al-Baghdadi and up to 330 other fighters on 28 May.
The Russian military said that the strike targeted an IS meeting held on the outskirts of Raqqa in northern Syria as IS leaders gathered to discuss the group’s withdrawal from their de facto capital.
There have been a number of previous reports of Baghdadi’s death.
According to a statement by Russia’s defense ministry published by the state-funded Sputnik news agency said 30 IS commanders and up to 300 soldiers were at the Raqqa meeting.
“According to information that is checked through various channels, IS leader Ibrahim Abu-Bakr al-baghdadi, who was killed as a result of the strike, was also present at the meeting,” it added.