The clashes raged through the night and into the morning on Saturday in the border region of Qalamun, said the so-called Syrian Observatory for Human Rights.
Syrian forces liberated most of the Qalamun region in April, with many insurgents withdrawing from the strategic area or slipping across the border in Lebanon.
But pockets of insurgents have remained in the mountainous region.
In another incident, a local chief of Nusra Front was killed in an apparent assassination after a bomb exploded in his car.
"Nusra's chief in Idlib (province), Yaacub al-Omar, was killed overnight when a bomb went off in his car near his house in the Khan al-Subul area," the Observatory said.
RA/NJF