The United States is "deeply concerned" about a recent flare-up of violence along Syria's northern border with Türkiye, a State Department spokesperson said Monday.

"Washington is deeply concerned about recent attacks along Syria's northern border and urges all parties to maintain ceasefire lines," said spokesperson Ned Price, days after increased bombardments in the area reportedly killed at least 21 civilians – including children.

"We deplore the civilian casualties in Al-Bab, Hassakeh, and elsewhere," said Price, adding that the United States remained committed to ensuring "the enduring defeat" of Daesh and a political resolution to the Syrian conflict.

The recent bloodshed came against a backdrop of increased tensions pitting the PKK terrorist group's Syrian wing, the YPG, against Turkish troops and their Syrian proxies.

The Britain-based Syrian Observatory for Human Rights, a war monitor with a broad network of sources on the ground, confirmed the toll.

In Al-Bab, a town under the control of Syrian factions loyal to Ankara, "artillery fire on a market by pro-regime forces killed 17 civilians – including six children – and wounded another 35," the Observatory said.

An Agence France-Presse (AFP) correspondent said the strike on the town near the Syria-Türkiye border had ripped through a market, describing it as a jumble of body parts, strewn vegetables and mangled handcarts.

The PKK is a designated terrorist organization in the United States, Türkiye and the European Union, and Washington's support for its Syrian affiliate has been a major strain on bilateral relations with Ankara.

The U.S. primarily partnered with the YPG in northeastern Syria in its fight against the Daesh terrorist group. On the other hand, Türkiye strongly opposed the YPG's presence in northern Syria. Ankara has long objected to the U.S.' support for the YPG, a group that poses a threat to Türkiye and that terrorizes local people, destroying their homes and forcing them to flee.

Under the pretext of fighting Daesh, the U.S. has provided military training and given truckloads of military support to the YPG, despite its NATO ally's security concerns. Underlining that one cannot support one terrorist group to defeat another, Türkiye conducted its own counterterrorism operations, over the course of which it has managed to remove a significant number of terrorists from the region.