The US-led coalition battling the Islamic State group said Friday it could not confirm the death of the jihadists' leader following reports by the Russia army that he might have been killed.

"We cannot confirm these reports at this time," said US Army Colonel Ryan S. Dillon, spokesman for the coalition's Operation Inherent Resolve in Syria and Iraq.

The Russian army said earlier that it hit IS leaders in an air strike in Syria last month and was seeking to verify whether IS chief Abu Bakr al-Baghdadi had been killed.

It said it had informed Washington of the May 28 strike near the jihadists' Syria stronghold of Raqa, which is now under assault by US-backed fighters.

"Senior commanders of the military groups of the so-called IS military council, 30 mid-ranking field commanders and up to 300 militants who provided security for them were eliminated," it said.

"According to information which is being checked through various channels, the leader of ISIL (IS) Ibrahim Abu-Bakr al-Baghdadi was also present at the meeting and was eliminated by the strike."