Turkey will soon move forward with its long-planned military operation to create what it calls a "safe zone" in northern Syria and US forces will not support or be involved in it, the White House press secretary said.
The statement came after Turkish President Tayyip Erdogan and US President Donald Trump discussed in a phone call Turkey's plans to establish a "safe zone" east of the Euphrates River in Syria.
Mr Erdogan said on Saturday a military incursion into northeastern Syria was imminent, after Turkey accused the US of stalling efforts to establish a "safe zone" there together.
Turkey has long vowed to carry out an operation targeting the Syrian Kurdish YPG militia, which it considers a terrorist organisation tied to Kurdish insurgents in Turkey. The US helped the YPG defeat Islamic State militants in Syria.
"Turkey will soon be moving forward with its long-planned operation into Northern Syria," the White House press secretary said in a statement.
"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," it added.
In the first Turkish comment following the statement, Mr Erdogan's spokesman Ibrahim Kalin said Turkey's "safe zone" plan was within the framework of Syria's territorial integrity.
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"The safe zone has two aims: to secure our borders by clearing away terrorist elements and to achieve the return of refugees in a safe way," Mr Kalin wrote on Twitter.
"Turkey is powerful and determined," he added.
Turkey says it wants to settle up to two million Syrian refugees in the zone.
It currently hosts 3.6 million Syrians sheltering from the more than eight-year conflict in their homeland.
...figure the situation out, and what they want to do with the captured ISIS fighters in their "neighborhood." They all hate ISIS, have been enemies for years. We are 7000 miles away and will crush ISIS again if they come anywhere near us!— Donald J. Trump (@realDonaldTrump) October 7, 2019
After the Erdogan-Trump phone call, the Turkish presidency said the two leaders had agreed to meet in Washington next month.
It said that during the call Mr Erdogan had expressed his frustration with the failure of US military and security officials to implement the agreement between the two countries.
The White House statement said "Turkey will now be responsible for all ISIS fighters in the area captured over the past two years", as France, Germany and other European nations from which they came refused US requests to take them back.
The NATO allies agreed in August to establish a zone in northeast Syria along the border with Turkey.
Turkey says the US, which supports the Syrian Democratic Forces (SDF), a YPG-led force that defeated Islamic State fighters in Syria, has moved too slowly to set up the zone.
It has repeatedly warned of launching an offensive on its own into northeast Syria, where US forces are stationed alongside the SDF.
The two countries are also at odds over how far the zone should extend into Syria and who should control it. Turkey says it should be 30km deep.
Ties between the allies have also been pressured over Turkey's purchase of Russian S-400 defence missiles and the trial of local US consulate employees in Turkey.