Following the significant advances by the Syrian army forces in nearby Idlib over the last week, Turkish-backed Syrian rebels attacked government-held positions northeast of Aleppo on Saturday.
The attack was focused on territory near the city of al-Bab, which has been controlled by Turkey and its Syrian opposition allies since 2017.
Syrian state media made no mention of a new attack.
Turkish forces were not taking part, rebel sources said.
Rebel sources said their fighters had taken three villages so far.
The Syrian Observatory for Human Rights, which monitors the war, described it as a fierce attack “carried out by factions loyal to Ankara”.
Syrian government forces, backed by Russian air power, have made rapid advances in Idlib this week, capturing the town of Maarat al-Numan which is located about 100 km southwest of al-Bab.
The government’s latest Idlib advance has triggered a fresh wave of civilian displacement, with hundreds of thousands moving towards the Turkish border.
Turkey, which already hosts 3.6 million refugees from Syria, fears a fresh wave of migrants from Idlib.
It has 12 military observation posts around Idlib, set up under a 2017 agreement with Russia and Iran, and several of them have since been surrounded by advancing Syrian government forces.
