Any additional support given by the United States to Syrian Kurdish YPG fighters will cause problems for Turkey, Prime Minister Binali Yildirim was quoted as saying on Friday.
Speaking to reporters on his return flight from Vietnam, Yildirim also said Turkey was working in cooperation with Russia and Iran in Syria, and there should be no reason for the United States and Turkey to be on opposite sides.
"We are talking about two NATO nations, there should be no reason for there to be [problems]. Of course, if they show a stance other than what they have told us on the YPG issue, it would be a problem," Yildirim was quoted as saying by broadcaster NTV.
Relations between Ankara and Washington have been tested by differences over Syria, where the United States is arming Kurdish YPG forces against Daesh (ISIS). Turkey sees the YPG as an extension of the outlawed Kurdistan Workers Party (PKK), which has waged a three-decade insurgency against Turkey.
The U.S.-backed operation to dislodge Daesh from their stronghold of Raqqa in Syria has also raised security concerns for Turkey. Ankara fears the YPG will change the demographics of Raqqa, and has repeatedly warned it would retaliate if faced with any cross-border threat.
Yildirim also said Turkey did not plan any further operations into Syria's Afrin and Idlib provinces.
Earlier in August, Turkish Foreign Minister Mevlut Cavusoglu had said Russia understands Ankara's stance on the YPG better than the United States, signaling an increasing drift between the NATO allies.
Yildirim said Turkey and Russia had reached an agreement on the procurement of S-400 missile defence system from Russia, and that the final decision would be made by the executive committee of Turkey's defence industry.
President Tayyip Erdogan had said late in July that Russia and Turkey had made progress in the plans to procure the S-400s and that signatures had been signed.
