(CNN)—Russia's Defense Ministry says it is investigating reports that ISIS leader Abu Bakr al-Baghdadi was killed in one of its airstrikes in Syria last month.
The airstrike on May 28 was carried out on the outskirts of the militant group's de facto capital Raqqa, on a command post where ISIS leaders were meeting, according to a ministry statement.
"According to information that is being verified through various channels, the leader of ISIS ... Abu Bakr al-Baghdadi was also present at the meeting and was killed as a result of the strike," the ministry said.
US defense officials said they were unable to confirm the reports. Col. Ryan Dillon, a spokesman for the US-led coalition's operation against ISIS in Syria and Iraq, said the coalition "cannot confirm these reports at this time."
There have been multiple reports of Baghdadi's death in the past that have turned out to be false.
The Russian statement said that the strike targeted ISIS leaders as they met to discuss their exit from the city through the so-called southern corridor. It also claimed that about 30 mid-level field commanders and up to 300 militants acting as bodyguards were also present.
The airstrike was carried out following drone footage confirmation of the meeting location, the statement said.
CNN Senior International Correspondent Clarissa Ward warned that the details provided by the Russians were inconsistent with the typical behavior of ISIS leaders.
"They do not meet in big groupings like that because of drone strikes, because they are constantly being bombarded," she said.
"If he has been killed, of course it would deal a big blow to the group, but let's just look at the past few weeks -- we've had major terror attacks in London, in Baghdad, in Tehran, in Kabul. So clearly it is still business as usual for ISIS."
CNN military analyst Lt. Gen. Mark Hertling also warned against giving too much weight to Russia's sources.
"I'm not going to take this too seriously because there have been at least five reported killings of al-Baghdadi over the last three years," he said.
"I wouldn't believe the Russian sources based on anything they're hearing out of Syria."
Al-Baghdadi: An elusive and brutal leader
Officials had long described the ISIS leader as enemy No. 1 in the fight against ISIS, and speculation had swirled over his whereabouts.
Baghdadi has kept a low profile, speaking out in occasional videos and audio messages.
He gave a sermon at a mosque in the Iraqi city of Mosul in 2014, in which he declared himself the leader of his envisaged Islamic caliphate. The sermon was filmed and widely watched around the world.
US forces captured him in Falluja, Iraq, in 2004. At the time, he was considered a low-level al Qaeda member.
He was freed in 2009, and within a year was the leader of Iraq's al Qaeda affiliate, heading up a renewed campaign of bombings and assassinations. Al Qaeda leaders later severed relations with him, saying he was insubordinate, killing too many civilians.
As the leader of ISIS, which has seized and lost swaths of territory in Iraq and Syria, he earned a reputation for brutality.
The extremist group brought a reign of terror and intimidation into areas where they gained control. And the brutality has continued, despite military setbacks. In one reported case, ISIS slaughtered 163 civilians and left their bodies in the street for days, the United Nations said.
US authorities offered a $25 million reward for information leading to his capture.
Abu Bakr al-Baghdadi, which is a nom de guerre, was born Ibrahim Awwad Ibrahim Ali al-Badri al Samarrai.