During their lightning advance on Damascus, the Islamist-led rebels seized all of Aleppo except for the two Kurdish-majority neighbourhoods of Sheikh Maksoud and Ashrafieh, which had long been controlled by Kurdish forces.

"A checkpoint belonging to the (Kurdish-led) Internal Security Forces in the Kurdish-majority Ashrafieh neighbourhood was attacked by Turkish-backed gunmen and explosive-laden drones, killing three security personnel and critically wounding seven," the Syrian Observatory for Human Rights said.

"This is the first attack of its kind in the area since the fall of the (Bashar al-Assad) regime," the Britain-based monitor added.

A Kurdish security official, who requested anonymity to discuss sensitive matters, told AFP that "pro-Turkey factions attacked the checkpoint with a suicide drone".

The Observatory said the two neighbourhoods were home to more than 300,000 civilians and expressed concern for their safety if Turkish-backed factions launched a full-blown assault.

"There are fears that those two Kurdish neighbourhoods might be besieged or attacked, which would be a big problem because many civilians live there," Observatory chief Rami Abdel Rahman told AFP.

Over the past month, clashes have flared between Turkish-backed factions and the Kurdish-led Syrian Democratic Forces (SDF), a US ally which played a major role in the war against the Islamic State jihadist group.

On Sunday and Monday, at least 31 combatants were killed in fighting between the two sides in Manbij district.

Turkey accuses the SDF's main component, the People's Protection Units (YPG), of links to the Kurdistan Workers' Party (PKK), which has waged a four-decade insurgency against the Turkish state.

On Sunday, Syria's de facto leader Ahmed al-Sharaa told Al Arabiya television that Kurdish-led forces should be integrated into the new national army.