Some 120 Islamic State fighters and 60 foreign mercenaries were killed in a series of Russian air strikes in Syria over the past 24 hours, the defence ministry in Moscow said on Saturday.
"A command post of the terrorists and up to 80 (IS) fighters including nine natives of the Northern Caucasus were destroyed in the area of Mayadeen," the ministry said, adding some 40 IS fighters were killed around the town of Albu Kamal.
As a result of an air strike more than 60 foreign mercenaries from the former Soviet Union, Tunisia, and Egypt were killed south of Deir Ezzor.
The ministry said the "large numbers of foreign mercenaries" were coming into the Syrian border town of Albu Kamal from Iraq.
Mayadeen is one of the Islamic State group's last bastions in Syria.
The advances against IS in Deir Ezzor have cost a heavy civilian death toll from Russian and coalition air raids.
The Britain-based Syrian Observatory for Human Rights said Russian air strikes on Thursday night killed 14 people, including three children, fleeing across the Euphrates on rafts near Mayadeen.
Russia has not acknowledged any civilian deaths from its strikes since it intervened in Syria in 2015, and dismisses the Observatory's reporting as biased.
Moscow has been carrying out air strikes in support of its ally Damascus targeting both IS in Deir Ezzor province and rival jihadists led by Al-Qaeda's former Syria affiliate in Idlib province in the northwest.
.Men inspect damages after an airstrike on the rebel-held city of Douma, in the eastern Damascus suburb of Ghouta, Syria, October 6, 2017.