Abu Bakr al Baghdadi is said to have been among 300 killed in the strike late last month
The Russian military has said it may have killed the leader of the Islamic State group in an airstrike.
Abu Bakr al Baghdadi was reportedly killed on 28 May along with other senior group commanders, according to the Russian defence ministry.
The ministry's statement was published by Russia's Sputnik news agency.
The strike is said to have targeted an IS meeting held on the outskirts of Raqqa as IS leaders gathered to discuss the group's withdrawal from their de facto capital.
More than 300 fighters were killed by the air raids, including 30 mid-level militant leaders, it said.
The death has not yet been confirmed by coalition forces.
If confirmed, al Baghdadi's death would mark a significant military achievement for Russia which has been active in Syria in support of President Bashar Assad since September 2015.
US-backed forces seized a western district of Raqqa earlier this month, just days after capturing an eastern part of the city.