The United States has told Turkey the Syrian Kurdish YPG militia would not remain in the region after an operation on Syria's Raqqa, Turkish Prime Minister Binali Yildirim said on Friday.

Speaking to reporters in London where he is on an official visit, Yildirim said a U.S. decision to provide weapons to Syrian Kurdish militants in the fight against Islamic State in Syria would harm the relations between the two NATO allies.

He said the United States had assured Turkey the region's demographics would not change as a result of this, a key concern for Ankara.

His comments were carried live on Turkish television.