US troops in northern Syria will no longer be near the border with Turkey, nor will they support Ankara's "long-planned operation" into the country, the White House said on Sunday.

"Turkey will soon be moving forward with its long-planned operation into Northern Syria. The United States Armed Forces will not support or be involved in the operation, and United States forces, having defeated the ISIS territorial 'Caliphate,' will no longer be in the immediate area," the White House said, using another acronym for the militant Islamic State (IS) group.

The statement, which followed US President Donald Trump's phone call with his counterpart Recep Tayyip Erdogan of Turkey, also criticised "France, Germany, and other European nations" for not repatriating their citizens detained in northern Syria who had joined IS.

"Turkey will now be responsible for all ISIS fighters in the area captured over the past two years in the wake of the defeat of the territorial 'Caliphate' by the United States," the statement said.

Meanwhile, Erdogan's spokesman today said the planned "safe zone" in northern Syria aims to clear terrorist elements from the border and return refugees safely to Syria within the framework of Syrian territorial integrity.

Earlier on Sunday, Erdogan and Trump agreed during a phone call to meet in Washington next month to discuss creating a "safe zone" in northern Syria, the Turkish presidency said.

Erdogan also expressed his "frustration over the US military and security bureaucracy's failure" to implement an August deal establishing a buffer zone on the Turkish border.

The day before, the Turkish leader warned that Ankara could launch a cross-border offensive "as soon as today, tomorrow".

Washington had previously sought to stop any Turkish operation against a US-backed Syrian Kurdish militia viewed by Ankara as a "terrorist" offshoot of Kurdish militants in Turkey.

The US worked closely with the People's Protection Units (YPG) militia to recapture swathes of territory from the IS militants.