At least 15 Ankara-backed Syrian fighters were killed Sunday after Kurdish-led forces infiltrated their territory in the country's north, the Syrian Observatory for Human Rights war monitor said.
Fighters from the Syrian Democratic Forces (SDF), who controls swathes of the country's northeast, "infiltrated positions of the Turkish-backed" fighters in the Aleppo countryside, said the Observatory, which has a network of sources inside Syria.
"The two sides engaged in violent clashes" that killed 15 of the Ankara-backed fighters, the monitor said.
An AFP correspondent in Syria's north said the clashes had taken place near the city of al-Bab, where authorities said schools would be suspended on Monday due to the violence.
The SDF is a US-backed force that spearheaded the fighting against the Islamic State group in its last Syria strongholds before its territorial defeat in 2019.
It is dominated by the Kurdish People's Protection Units (YPG), viewed by Ankara as an offshoot of the outlawed Kurdistan Workers' Party (PKK) which claimed the attack on Ankara.
Turkish troops and allied rebel factions control swathes of northern Syria following successive cross-border offensives since 2016, most of them targeting the SDF.