Turkey will carry out an operation east of the Euphrates river in northern Syria, in an area controlled by the Kurdish YPG militia, Turkish President Tayyip Erdogan said on Sunday.

Turkey has been running out of patience with the United States, which made an agreement with Ankara to implement a safe zone in northeastern Syria. Erdogan said both Russia and the United States have been told of the operation.

Following U.S. President Donald Trump's announcement last year of a planned U.S. withdrawal from northern Syria, the two NATO allies agreed to create a safe zone inside Syria along its northeastern border with Turkey, that would be cleared of the YPG militia.

The YPG was Washington's main ally on the ground in Syria during the battle against Islamic State, but Turkey sees it as a terrorist organisation.

Ankara says that the United States has stalled progress on setting up the safe zone and has demanded that Washington sever its relations with the YPG.

The operation, which would mark the third Turkish incursion into Syria in as many years, was first signalled by Erdogan earlier this year but later put on hold.

"We entered Afrin, Jarablus, and Al-Bab. Now we will enter the east of the Euphrates," Erdogan said on Sunday during a motorway-opening ceremony. "We shared this with Russia and the United States."