Turkey's military says it's "assessed" that Syrian government forces dropped barrel bombs on rebels in the north of the country, in an area where Turkey is backing opposition forces.
Two rebels were killed and five injured in the attack from a helicopter on Tuesday, according to a statement from the military carried by the Dogan news agency.
Turkey launched an invasion of northern Syria in August to attack both Kurdish forces and extremist group Islamic State, taking more than 900 square kilometres of territory.
Recently, clashes have intensified between the Turkey-backed rebels and Kurdish forces in the northern Aleppo countryside. The US has called on all sides to focus on fighting Islamic State. The Kurds have been Washington's main ally against the extremist group.
Last week, a Turkish airstrike on the Kurds resulted in dozens of casualties. The Syrian army subsequently warned it would down Turkish planes violating its airspace and then went further, saying it views any Turkish presence on its territory as an occupation.
Turkey has repeatedly warned the Kurds not to attempt to connect an isolated enclave in the north-west of Syria to their other areas in the centre and east.
On Saturday, President Recep Tayyip Erdogan said his army and the Turkey-backed rebels would push on to al-Bab, a city to the east of Aleppo currently controlled by Islamic State. The Kurds also want the city, which lies between their territories.
If the rebels take al-Bab and its surrounding villages, they could create a frontline with Syrian government forces east of Aleppo.
