BEIRUT — Russia claimed Friday it killed the leader of the Islamic State group in an airstrike targeting a meeting of IS leaders just outside the group’s de facto capital in Syria.

The Russian Defense Ministry said Abu Bakr al-Baghdadi was killed in a Russian strike in late May along with other senior group commanders.

There had been previous reports of al-Baghdadi being killed but they did not turn out to be true. The IS leader last released an audio on Nov. 3, urging his followers to keep up the fight for Mosul as they defend the city against a major offensive that began weeks earlier.

The spokesman for the US-led anti-IS coalition said in a statement Friday he could not confirm the Russian claim.

The report of al-Baghdadi’s death comes as IS suffers major setbacks in which they have lost wide areas of territory and both of their strongholds — Mosul in Iraq and Syria’s Raqqa. Both are under attack by various groups that are fighting under the cover of airstrikes by the US-led coalition.

US officials and Syrian activists say many commanders have fled Mosul and Raqqa in recent months for Mayadeen, a remote town in the heart of Syria’s IS-controlled Euphrates River valley near the Iraqi border.

The claim of al-Baghdadi’s possible demise also comes nearly three years to the day after he declared himself the leader of an Islamic caliphate in Iraq and Syria, from a historic mosque in Mosul.

If confirmed, it would mark a major military success for Russia, which has conducted a military campaign in support of Syrian President Bashar al-Assad since September 2015.

The Defense Ministry said the air raid May 28 that targeted an IS meeting held on the southern outskirts of Raqqa in Syria also killed about 30 mid-level militant leaders and about 300 other fighters.

The ministry said the IS leaders were gathered to discuss the group’s withdrawal from Raqqa, the group’s de facto capital. It said the military began planning the hit after getting word that the group’s leadership was to meet in order to plan IS’ exit to the south.

The Russian military sent drones to monitor the area and then dispatched a group of Su-34 bombers and Su-35 fighter jets to hit the IS gathering.

“According to the information that is being verified through various channels, IS leader Abu Bakr al-Baghdadi also attended the meeting and was killed in the airstrike,” the military said in a statement.

The Defense Ministry added that it had warned the US of the coming strike.

Syrian opposition activists reported airstrikes May 28 south of Raqqa that killed more than a dozen people.

The Britain-based Syrian Observatory for Human Rights, which tracks Syria’s war, said airstrikes on the road linking the villages of Ratla and Kasrat killed 18 people while the activist-operated Raqqa Is Being Slaughtered Silently said 17 civilians were killed in the airstrike on buses carrying civilians.

The Observatory said the dead included 10 Islamic State group members. It did not elaborate at the time.

The Russian ministry said that among other militant leaders killed in the raid were IS leaders Abu al-Khadji al-Mysri, Ibrahim al-Naef al-Khadj and Suleiman al-Shauah.

Al-Baghdadi declared a caliphate in Syria and Iraq in June 2014 days after his fighters captured Mosul, the largest city they ever held. The group has since horrified the world with atrocities in areas it held as well as attacks it claimed around the world that killed hundreds.

Al-Baghdadi is a nom de guerre for a man identified as Ibrahim Awwad Ibrahim Ali al-Badri al-Samarrai. The US is offering a $25 million reward for information leading to his death or capture.

Alexei Pushkov, head of the committee for information policies at the upper house of the Russian parliament, tweeted that, “if confirmed, al-Baghdadi’s death will be a powerful blow to the IS. It has been retreating on all fronts, and the death of its leader will accelerate its demise.”