Turkish warplanes attacked pro-Syrian government forces overnight, killing at least 17 people in a village in the north of the Afrin region in northwestern Syria, the British-based Syrian Observatory for Human Rights said on Friday.
The dead included three members of the Syrian Kurdish YPG force, while the rest came from militias that support President Bashar al-Assad and entered Afrin last week to help repel a Turkish offensive, the Observatory said.
The Turkish military declined to comment on the Observatory report, but the Turkish state-run Anadolu news agency reported on Friday that Turkish attack helicopters had killed nine YPG fighters in the west of Afrin.
Another Turkish news agency, Dogan, reported that Turkish and allied forces had started an operation on Friday morning to take control of the town of Rajo in Afrin.
Turkey and allied Syrian rebel groups began their operation against the YPG in Afrin in January, aiming to drive out the Kurdish militia, which Ankara sees as a terrorist group linked to an insurgency inside Turkey's borders.
Despite making slow progress at first, the offensive has gained control over all Afrin's border areas adjoining Turkey. Late on Thursday, the Turkish military said eight Turkish soldiers had been killed and 13 injured in clashes in Afrin.
Last month, after the YPG asked the Syrian government to send its army to repel the offensive, pro-Syrian government militias crossed into Afrin and deployed along the frontlines with Turkey.
However, the move did not deter the Turkish offensive and has not so far heralded any wider escalation involving the Syrian government and the forces that support it.