"As a result of a precision airstrike of the Russian air forces in the vicinity of Deir Ezzor city, a command post, communication centre and some 40 ISIS fighters have been killed," the Russian defence ministry said in a statement posted on Facebook.
"According to confirmed data, among the killed fighters are four influential field commanders including Deir Ezzor emir Abu Mohammed al-Shimali," the ministry said.
Gulmurod Khalimov, who is known as the IS group's Minister of War and the highest-ranking defector from ex-Soviet Tajikistan, suffered a "fatal injury," it added.
Russia's SU warplanes dropped "bunker buster" bombs on the fighters as they were meeting near Deir Ezzor to discuss how to respond to the advance of the Syrian army, Moscow said.
Backed by Russia, Syrian troops on Tuesday broke through a years-long siege imposed by IS militants on tens of thousands of civilians in Deir Ezzor.
Reports of Khalimov's death have surfaced before.
The Times said in April that Khalimov, described as the highest-ranking IS commander in Mosul, had been killed in an airstrike.
A former colonel, he headed the Tajik interior ministry's special forces unit and received American training before joining IS in 2015.
Khalimov pledged allegiance to the jihadist group in a video released in May 2015 in a high-profile defection that rocked Tajikistan, a mainly Muslim country.
In the footage he warned that he and other IS recruits based in the Middle East were "coming" for top officials in the country, including long-ruling President Emomali Rakhmon.
In 2016, the United States offered a $3 million bounty for information leading to his location or arrest.
In July, police in Tajikistan killed four relatives of the former special forces colonel in a gun battle, an interior ministry source has said, and three other relatives were detained.
The source claimed that all of those killed or detained were IS "supporters" and said that they were intending to flee to neighbouring Afghanistan, but did not offer any proof to back up the claims.