A wave of Russian airstrikes killed at least 21 "Daesh terrorists" in the Syrian desert over the past 24 hours, a monitor said Saturday.

The 21 were killed in at least 130 airstrikes "carried out over the past 24 hours by the Russian air force targeting (Daesh) in an area on the edge of the provinces of Aleppo, Hama and Raqqa," the Syrian Observatory for Human Rights said.

The raids, which continued into Saturday, follow a series of Daesh attacks Friday on the Bashar Assad regime and allied forces that killed at least eight members of a pro-Assad militia, the U.K.-based monitor said.

In recent months, the vast desert, known in Arabic as the Badia, has been the scene of increasingly frequent fighting between Daesh terrorists and regime forces backed by Russian air power.

Daesh overran large parts of Syria and Iraq and proclaimed a cross-border "caliphate" in 2014 before multiple offensives in the two countries led to its territorial defeat.

The terrorists continue to launch attacks, mostly in the Badia desert which stretches from the central province of Homs to the border with Iraq.

More than 1,300 government troops have been killed in these clashes, as well as 145 pro-Iran militia members and more than 750 Daesh terrorists, according to the Observatory.

Since Syria's civil war broke out in 2011, more than 387,000 people have been killed and millions forced from their homes.