A spokesman for the U.S.-backed force fighting the Islamic State group in eastern Syria says fighters are advancing on two fronts amid intense fighting with the extremists in the last area they control.

Mustafa Bali of the Kurdish-led Syrian Democratic Forces tweeted Saturday that "heavy clashes" are taking place in the area on the east bank of the Euphrates River.

Bali said three SDF fighters were wounded.

The SDF on Friday evening resumed military operations to liberate the last piece of territory held by IS in the province of Deir el-Zour after evacuating thousands of civilians and hostages who had been besieged inside.

Zana Amedi, an SDF commander, told The Associated Press that "an active ground force" is advancing into IS-held territories as the extremists resort to sniper fire and booby-traps.