Clashes in the Syrian Desert between pro-government forces and holdouts of the Daesh terror group have killed at least 90 combatants this month, a war monitor said on Wednesday.

Russian aircraft carried out strikes in support of their Syrian government ally, the Syrian Observatory for Human Rights said.

The clashes broke out in two separate areas of the vast desert that separates the Orontes valley in the west from the Euphrates valley in the east.

The government side lost 41 dead, the extremists 49, the Britain-based war monitor said.

At least 10 government loyalists and 13 Daesh terrorists were killed over the past 24 hours alone, observatory head Rami Abdul Rahman said.

Mobile Daesh units have remained active in the Syrian Desert, known in Arabic as the Badia, since the jihadists lost the last shred of its self-proclaimed caliphate in March last year.

September clashes killed 13 pro-government fighters and 15 extremists, while in early July 20 pro-government fighters and 31 jihadists were killed over two days.

In August, Daesh claimed an attack, presumably mounted from the desert, that killed a Russian general near the Euphrates valley city of Deir Ezzor