MOSCOW (AFP) - Russia's military on Wednesday (Aug 31) said its air strikes had killed top the Islamic State in Iraq and Syria (ISIS) group strategist Abu Mohamed al-Adnani, after Washington said coalition forces had targeted the militant propaganda chief.

In a statement, Russia's defence ministry said an Su-34 warplane on Tuesday killed "up to 40" ISIS fighters in a bombing raid near the village of Um Hosh in the province of Aleppo.

Russia has been flying its own bombing campaign in Syria in support of leader Bashar al-Assad since September but this is first time they have claimed to have killed a top-ranking ISIS leader.

"According to information confirmed through several intelligence channels, field commander Abu Mohamed al-Adnani was among those killed," the statement said.

The ISIS-affiliated Amaq news agency announced propaganda chief Adnani's death late on Tuesday, saying he "was martyred while surveying operations to repel the military campaigns against Aleppo" in northern Syria.

The United States said coalition forces had targeted Adnani, who had a US$5-million (S$6.8 million) bounty on his head, in an air strike in Aleppo province on Tuesday and that the Pentagon was still assessing the result.

His death will be a major blow to ISIS, which has suffered a series of setbacks this year including territorial losses in Syria and Iraq and the killings of other top figures.

Adnani, a Syrian born in 1977, was one of ISIS's most recognised leaders, at the heart of a sophisticated propaganda and recruitment machine that produced slick videos and sustained a huge social media presence.