Turkish-backed forces launched an offensive against the SDF in November that has seen them capture several Kurdish-held enclaves in the north despite US efforts to broker a ceasefire.

The US-backed SDF spearheaded the military campaign that ousted the Islamic State jihadist group from its last territory in Syria in 2019 but Ankara accuses its main component, the People's Protection Units (YPG), of ties to Turkey's outlawed Kurdistan Workers' Party (PKK).

SDF spokesman Farhad Shami told AFP that a Turkish strike on a popular market in the Sarrin area killed 12 people on Tuesday, updating an earlier toll of six.

Shelling of two other areas on Monday and Tuesday killed six more, he added.

Britain-based war monitor the Syrian Observatory for Human Rights said the fighting has killed 521 people since December, 56 of them civilians.

It said the dead also included 77 SDF troops and 388 pro-Turkey fighters.

Earlier this month, then-US secretary of state Antony Blinken said he was working to address Turkey's concerns and dissuade it from stepping up its offensive against the SDF.

In a call with Turkish Foreign Minister Hakan Fidan last week, Blinken's successor Marco Rubio reiterated the "need for an inclusive transition in Syria", State Department spokeswoman Tammy Bruce said.