Turkey-backed Syrian rebel groups clashed with government forces near a city in northern Syria they captured from Islamic State, the second such confrontation in that region this month.
The clash late on Sunday took place in an area where the sides are waging separate campaigns against Islamic State.
Russia, which backs the Syrian government, intervened to halt the previous clash.
The latest incident occurred near the city of al-Bab, which the Free Syrian Army (FSA) rebels captured last week from Islamic State. Syrian government forces on Sunday announced the capture of the town of Tadef, 4 km (2.5 miles) to the south.
A rebel official in touch with one of the FSA groups taking part in the Turkey-backed campaign in northern Syria said rebels had opened fire on Sunday in response to an attempt by government forces to advance towards an area near al-Bab.
An FSA statement said "22 regime members" were killed.
A Syrian military source said the rebels had "targeted our forces in Tadef with artillery and machine guns". The source, who described the FSA factions as "terrorist groups that belong to Turkey", gave no casualty toll.
Earlier this month, a senior Russian official said Tadef marked an agreed dividing line between the Syrian army and the Turkey-backed forces.
Turkey, a major backer of Syrian opposition to President Bashar al-Assad, last year began cooperating with Russia in Syria. With Moscow, it has co-sponsored a ceasefire agreement between government and rebel forces in western Syria.
The rebel official said Turkish forces were not involved in the confrontation, adding that government forces appeared to be testing the rebels. "They probably hadn't thought that they would receive such a fierce response," said the official.
The Syrian military source said the incident showed the rebels' "main aim is not fighting Daesh (Islamic State), but realising other goals including an attempt to obstruct the Syrian army's operation confronting Daesh".
