The likelihood that Islamic State leader Abu Bakr al-Baghdadi has been killed is close to 100 percent, Interfax news agency quoted the head of the defence committee in Russia's upper parliamentary house as saying on Friday.
Russia's defence ministry said a week ago it believed it may have killed Baghdadi when one of its air strikes hit a gathering of senior Islamic State commanders on the outskirts of the Syrian city of Raqqa.
But armed groups fighting in the region and US officials say they have no evidence that Baghdadi was killed, and many regional officials have said they are sceptical about the information from Moscow.
There had been previous reports of al-Baghdadi being killed but they did not turn out to be true. The ISIS leader last released an audio on 3 November, 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-ISIS coalition said in a statement Friday he could not confirm the Russian claim.
The report of al-Baghdadi's death comes as ISIS 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 who 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 ISIS-controlled, Euphrates river valley near the Iraqi border.
If confirmed, it would mark a major military success for Russia, which has conducted a military campaign in support of Syrian President Bashar Assad since September 2015.
The Defense Ministry said the air raid on 28 May that targeted an ISIS 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 ISIS 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 the word that the group's leadership was to meet in order to plan ISIS' 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 gathering.
According to the information that is being verified through various channels, ISIS leader Abu Bakr al-Baghdadi also attended the meeting and was killed in the airstrike.Russian military in a statement
The Defense Ministry added that it had warned the US of the coming strike.
Syrian opposition activists reported airstrikes on 28 May south of Raqqa that killed more than a dozen people.
(The story has been edited for length)
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