Jaish Osoud al-Sharqiya killed 15 regime troops in the Syrian desert, known as al-Badiya, when its artillery and Grad rockets pounded an army stronghold in Um Remam area, spokesman said Friday.
Said Seif, press officer of the U.S.-backed group that operates in eastern Qalamoun and al-Badiya, said 141 Grad rockets were fired on the regime bastion in the strategic Um remam area near the Iraqi border.
The surprise attack has left heavy losses in regime ranks, destroying ten armoured vehicles, he added.
Also in the desert, the regime army has reached Sukhneh, the last extremist-held town on the road to its besieged garrison in the east, the Syrian Observatory for Human Rights said on Friday.
Regime forces are on the outskirts of Sukhneh, some 70 kilometres northeast of the famed ancient city of Palmyra, the Syrian Observatory for Human Rights said.
The town is the last on the desert road to the eastern city of Deir al-Zor, where a government garrison has held out under siege by Daesh (ISIS) since early 2015.
Sukhneh and the oil and gas fields in the surrounding countryside have been held by Daesh since 2015.
"Heavy fighting is ongoing between the two sides, with regime artillery and rocket fire," Observatory director Rami Abdel Rahman said.
He said Russian warplanes were supporting the government advance.
ISIS commanders fled into the surrounding mountains as the army neared the town, he added.
Since May, the Army has been conducting a broad military campaign to recapture the vast desert that separates the capital Damascus from Deir al-Zor and other towns along the Euphrates Valley.
Already defeated in its Iraqi bastion of Mosul, Daesh is facing multiple assaults in Syria.
The U.S.-backed Syrian Democratic Forces now control more than half of its most important remaining stronghold Raqqa.
