An air strike hit a training centre for the SDF’s local Asayish security forces, the Syrian Observatory for Human Rights said in a statement.
The SDF confirmed “a number of our forces were killed and others wounded” in the strike, the latest in a series of bombing raids conducted by Turkey since Thursday.
Authorities in the area had called for blood donations, while hospitals were full of casualties.
Turkey has intensified its air strikes on Syria’s Kurdish-held northeast following a bomb attack in Ankara last week that was claimed by the Kurdistan Workers’ Party (PKK).
The SDF is mainly dominated by the People’s Protection Units (YPG) which Turkey considers an extension of the PKK.
However, the SDF has denied that those behind the Ankara attack had passed through the area.
Washington has used the SDF as its primary partner in Syria in the fight against the Islamic State group since 2014, though it considers the PKK a terror group.
A top Turkish official stated on Friday that his country wouldn’t stop pursuing “terror groups” or bow to threats following the downing of a Turkish drone by US forces in Syria.
“We will eradicate terrorism, whether in northern Iraq, northern Syria or anywhere else,” Fahrettin Altun, the Turkish president’s communications director, said, adding, “We will not bow to threats and we will not compromise our security.”
The downing of the drone on Thursday marked the first-ever NATO-on-NATO armed clash in Syria.