Turkey has for weeks threatened to launch a vast cross-border offensive against the People's Protection Units (YPG), which controls most of northeastern Syria.

Ankara considers the Syrian offshoot of the Kurdistan Workers Party (PKK) to be a terrorist organisation.

The head of Hayat Tahrir al-Sham (HTS), Abu Mohammad al-Jolani, did not offer direct military support but made clear he supported the YPG's removal from eastern Syria, where it has been battling the Islamic State (IS) group.

"We consider the PKK to be an enemy of this revolution. It controls areas inhabited by large numbers of Sunni Arabs," he told the HTS-affiliated Amjad media outlet, referring to the YPG.

The YPG extended its influence beyond Kurdish heartlands in northeastern Syria when it took the lead role in the US-backed ground battle against IS.

"We are in favour of this region being liberated from the PKK," Jolani said.

"We would not stand in the way of an operation against an enemy of the revolution."

HTS recently took full control of the Idlib region in northern Syria after deadly fighting with other factions backed by Turkey.

Jolani has tried to cast himself as a leader of the anti-regime camp but many opposition factions blame him for tarnishing the image of the rebellion against the rule of Syria's President Bashar al-Assad and ultimately causing its failure.

Since Russia threw its military might behind him in 2015, Assad has reclaimed much of the ground lost in the first years of Syria's conflict.