At least six Syrian regime fighters were killed as heavy clashes broke out Tuesday between the army and Turkish forces for the first time since Ankara attacked northeastern Syria three weeks ago, a war monitor said.

The Syrian Observatory for Human Rights said artillery and machine-gun fire was exchanged near Assadiya, south of the border town of Ras al-Ain.

"Heavy fighting erupted for the first time between the Syrian and Turkish armies," the Britain-based monitoring group said.

The Turkish military and its Syrian proxies attacked Kurdish forces in northeastern Syria on October 9 with the aim of creating a roughly 30-kilometre (20-mile) deep buffer zone.

"Turkish artillery fire killed five regime forces in battles on the edge of the village of Assadiya," Rami Abdel Rahman, the head of the Observatory, told AFP.