The defence ministry’s statement came a day after Russia said it may have killed the terrorist group’s leader Abu Bakr al-Baghdadi in an air strike last month.

The US government, which is leading a separate bombing campaign, said it could not corroborate Baghdadi’s death and Western and Iraqi officials were sceptical.

Russia claimed it killed around 180 militants and the two commanders al-Beljiki and al-Masri in bombing close to the Isis stronghold of Deir ez-Zor on 6 and 8 June.

Hisham al-Hashimi, a Baghdad-based expert who advises several Middle Eastern governments on Isis affairs, said he was sceptical about Russia’s claim on Saturday.

He said Abu Yassin al-Masri is the same person as Abu al-Haj al-Masri, who the Russians on Friday said they killed near Raqqa in May.

In pictures: Mosul offensive

Mr Hashimi said the other Isis leader, al-Beljiki, was unlikely to have been in Syria at the time of the attack.

“The Russians are trying to improve their record fighting Daesh [Isis] as it was the Americans who have killed the top commanders of the group so far, like Abu Omar al-Shishani, Abu Muslim al-Turkmani, Abu Mohammed al-Adnani and Abu Ali al-Anbari,” he said.

“If Russia’s announcements prove wrong, their credibility will be hurt.”

Isis fighters are close to defeat in the twin capitals of the group’s territory, Mosul in Iraq and Raqqa in Syria, after nearly three years ruling over millions of people in a wide area in both countries.

A US-led coalition is assisting Iraqi forces in the Mosul battle and supporting the Syrian Democratic Forces (SDF), which includes Arab and Kurdish militias, in Raqqa amid concern over civilian casualties.

Having been forced into retreat across much of Syria, Isis’ biggest remaining foothold in Syria is in the eastern province of Deir ez-Zor, where Russia is supporting a group offensive by troops loyal to President Bashar al-Assad.

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