The U.S. move to establish a 30,000-strong boarder force from the PKK terrorist group's Syrian affiliate Democratic Union Party's (PYD) armed People's Protection Units (YPG) has caused concern over both Iran and Russia.

Iranian President Hassan Rouhani said yesterday that the new U.S.-backed force in Syria would "fan the flames of war," echoing the vehement response from Ankara and Moscow to the plan.

Russian Foreign Minister Sergei Lavrov condemned the move Monday, saying the formation of a YPG-controlled zone could pose a threat to the territorial integrity of Syria.

Russia started to withdraw its forces from Syria last month, but Moscow has said it would keep its Khmeimim Air Base in Syria's Latakia province as well as its naval facility at Tartos "on a permanent basis."

Lavrov and Iranian Foreign Minister Mohammad Javad Zarif discussed the conflict in Syria in a phone conversation, the Russian Foreign Ministry said yesterday.

The Syrian regime also responded by vowing to crush the new force and drive U.S. troops from Syria. Russia called the plans a plot to dismember Syria and place part of it under U.S. control, and Turkey described the force as a "terrorist army." Iranian Foreign Ministry spokesman Bahram Qasemi said such a force would raise tensions in Syria. Iran supports Bashar Assad in the nearly seven-year civil war against rebel forces and Daesh militants, sending weapons and soldiers. "The U.S. announcement of a new border force in Syria is an obvious interference in the internal affairs of this country," Qasemi was quoted as saying by the state-run IRNA news agency. Qasemi urged all U.S. forces to leave Syria immediately.