A Syria war monitoring organization says an Islamic State group attack in the country's center has killed scores of government troops.

The Islamic State group lost its last territories in Syria in March after months of battles with U.S-backed fighters in the east. But the militants remain active in the desert area where they have increasingly targeted government troops.

The Syrian Observatory for Human Rights said Saturday IS militants ambushed government forces in the desert of central Homs province, setting off Thursday night two days of clashes that killed at least 27 soldiers.

Liwa al-Quds, a pro-government militia, said IS militants attacked two army battalions in the area. It said its fighters liberated the battalions and pulled out the bodies but didn't give a casualty figure.