The Russian Defense Ministry says the leader of the extremist group Islamic State (IS), Abu Bakr al-Baghdadi, may have been killed in a Russian air strike in Syria late last month.
The ministry said on June 16 that it is checking information suggesting that Baghdadi was killed in an air strike on the southern outskirts of Raqqa early on May 28.
The U.S. Defense Department said it had no information confirming that Baghdadi had been killed in a Russian air strike.
"We have no information to corroborate those reports," Pentagon spokesman Navy Captain Jeff Davis said.
Russian Foreign Minister Sergei Lavrov said he did not have "100 percent confirmation," and the Kremlin declined to comment directly.
The Russian Defense Ministry said the strike killed about 330 people, including several senior IS figures.
It said the strike targeted a meeting at which IS members were discussing routes out of Raqqa, a main IS stronghold where the extremist group is under pressure from an offensive by U.S.-backed Syrian forces.
The attack was launched after Russian forces in Syria learned of the meeting ahead of time, the ministry said on Facebook.
"According to information that is now being checked via various channels, also present at the meeting was Islamic State leader Abu Bakr al-Baghdadi, who was eliminated as a result of the strike," it said.
The United States was informed in advance about the place and time of the strike, the Russian military said.
IS overran large parts of Syria and northern Iraq in 2014, terrorizing civilians and carrying out atrocities.
Its fighters now appear close to defeat in their main strongholds -- Raqqa in Syria and Mosul in Iraq.
Russia and the United States, which back opposing sides in the six-year-old war in Syria, are conducting separate air campaigns.
The U.S.-led coalition is targeting IS militants, while Western officials say Russian strikes have mainly targeted other opponents of Syrian President Bashar al-Assad's government.
Russia has given Assad crucial military and diplomatic aid throughout the war, which started with a government crackdown on protests in 2011 and has killed more than 400,000 people.
The most recent public video footage, from 2014, shows Baghdadi declaring his "caliphate" from the pulpit of Mosul's Grand al-Nuri mosque.
Baghdadi -- a 46-year-old Iraqi born Ibrahim al-Samarrai -- broke away from Al-Qaeda in 2013.
The director of the Britain-based Syrian Observatory for Human Rights cast doubt on the report Baghdadi may have been killed, telling the Reuters news agency that according to his information Baghdadi was in another part of Syria at the end of May.
"The information is that as of the end of last month Baghdadi was in Deir al-Zor, in the area between Deir al-Zor and Iraq, in Syrian territory," Reuters quoted Rami Abdulrahman as saying.