BEIRUT: Syrian government forces and their allies advanced against Daesh (ISIS) militants in countryside east of Raqqa on Thursday, war monitors reported.

The advance, to within 4 km of the town of Maadan, crossed the provincial boundary between Raqqa and Deir al-Zor for the first time from the west, the Britain-based Syrian Observatory for Human Rights said.

The monitoring group has reported recent advances in the area by the Syrian army, nearing territory controlled by U.S.-backed forces who are separately fighting Daesh in their stronghold of Raqqa city.

Incidents involving the U.S.-backed forces and pro-Damascus forces last month caused tension between Washington and Syrian government ally Moscow.

Daesh is losing ground fast in Syria to separate campaigns waged by the Russian-backed Syrian government on the one hand, and U.S.-backed regional Kurdish forces and their allies on the other.

Deir al-Zor province, which borders Iraq to the east, is almost entirely under Daesh control. The Syrian government has clung to a pocket of territory in Deir al-Zor city, the provincial capital, and at a nearby air base.