The Turkish military said on Friday 71 members of a Kurdish militia had been killed in Syria in the last week in what appeared to mark an escalation of clashes with the U.S.-backed YPG group vying for control of areas along Turkey's border.

Clashes between Turkish-backed forces and the YPG militia, both allies of the United States in fighting Islamic State, threaten to hamper U.S. efforts to forge a coalition to seize the militants' stronghold of Raqqa.

Turkey is alarmed Washington is veering towards a tie-up with YPG in operations to seize Raqqa, to the exclusion of its forces. Washington says it is taking steps to avoid conflict between Turkish forces and YPG, which Ankara deems terrorist for its links with PKK Kurds fighting on Turkish soil.

The United States and the European Union also regard the Kurdistan Workers Party (PKK) as a terrorist group.

Turkey's army, backing an alliance of Syrian-Arab and Turkmen fighters, said 71 Kurds from the YPG and the Kurdish group fighting the Turkish state, the Kurdistan Workers Party, had been killed over a week. This was included in a total of 134 since Jan. 5.

The volatile situation in northern Syria is further complicated by advances from the south by forces fighting for President Bashar al-Assad.

Syrian state media quoted a military source late on Thursday as saying Turkey's military had shelled Syrian government forces and their allies, causing deaths and injuries.

State-run SANA news agency quoted the military source as saying that the Turkish bombardment targeted Syrian border guard positions in the countryside near the northern city of Manbij.

The area around Manbij has been controlled since last year by the Manbij Military Council, a local militia that is a part of the Syrian Democratic Forces (SDF), an umbrella organisation of armed groups of which the YPG is also a part.