A car bomb killed a dozen people and injured 30 on Saturday in a market of a Syrian border town that Turkish-backed forces seized last month, prompting Ankara to blame the Kurdish YPG militia it had targeted in its incursion.
The Syrian Observatory for Human Rights said pro-Turkey fighters and civilians were among the dead and injured in Tel Abyad. Turkey's state-owned Anadolu Agency said 13 were killed after a "bomb-laden vehicle" exploded.
Tel Abyad is one of two major border towns that saw the heaviest fighting when Ankara launched the incursion on October 9 against the Syrian Kurdish YPG that drew international condemnation. The YPG had for years been allied to the United States in the fight against Daesh.
The explosion comes after two weeks of relative calm in northeastern Syria, and a day after Turkish and Russian troops began joint ground patrols under a deal between the two countries that pushed the YPG from Turkey's border.
While Moscow has said the YPG have withdrawn to at least 30 km (18 miles) from the border under the deal, Ankara has been sceptical and held out the possibility of new attacks if members of what it sees as a terrorist group remain.
"We condemn this inhuman attack of the bloody PKK/YPG terrorists who attacked the innocent civilians of Tel Abyad who returned to their homes and lands as a result of the Operation Peace Spring," Turkey's defence ministry said on Twitter.
Turkey's presidential spokesman Ibrahim Kalin also pointed the finger at the YPG.
A spokesman for the Syrian Democratic Forces, which includes the YPG, was not immediately available for comment.
The Kurdistan Workers Party (PKK), based in Turkey, is designated a terrorist group by Turkey and its Western allies. Ankara considers the YPG a terrorist group because of its ties to PKK Kurdish militants in southeast Turkey.