In a statement, Russia's defence ministry said an Su-34 warplane yesterday killed "up to 40" IS 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 IS leader.
"According to information confirmed through several intelligence channels, field commander Abu Mohamed al-Adnani was among those killed," the statement said.
The United States said coalition forces had targeted Adnani, who had a USD 5-million bounty on his head, in an air strike in Aleppo province yesterday and that the Pentagon was still assessing the result.
His death will be a major blow to IS, 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 IS'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.