Donald Trump has launched a harsh attack on Turkey, threatening to "totally destroy and obliterate" its economy if it takes a planned military strike in Syria too far.
Turkey is expected to invade the border area after US troops began withdrawing from the war-torn country on Monday, with Mr Trump saying it was "time to get out of these ridiculous endless wars".
Amid criticism over his decision, Mr Trump has said he would destroy the Turkey's economy if it steps out of line in Syria.
He wrote on Twitter: "As I have stated strongly before, and just to reiterate, if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the economy of Turkey (I've done before)."
Mr Trump added: "They must, with Europe and others, watch over the captured ISIS fighters and families.
"The US has done far more than anyone could have ever expected, including the capture of 100% of the ISIS Caliphate.
"It is time now for others in the region, some of great wealth, to protect their own territory. THE USA IS GREAT!"
Speaking later at the White House, Mr Trump said he had told Turkish President Tayyip Erdogan in a phone call that Turkey could suffer the "wrath of an extremely decimated economy" if it acted in Syria in a way that was not "humane."
It comes after Syria's Kurds accused the US of turning its back on its allies ahead of the expected Turkish assault.
Syrian Kurdish fighters warned that Washington's abrupt decision to stand aside - announced by the White House late on Sunday - will overturn years of achievements in the battle against militants from so-called Islamic State.
In a strongly worded statement, they accused Washington of failing to abide by its commitments to its key allies.
President Tayyip Erdogan also spoke hours after the White House said US forces will move aside.
"Following our conversation last night (with US President Donald Trump), the withdrawal has started as expressed by the president," the Turkish leader said.
Mr Erdogan did not elaborate on the planned Turkish incursion but said Turkey was determined to halt what it perceives as threats from the Syrian Kurdish fighters.
The White House, in a statement that was silent on the fate of Kurds, said US troops "will not support or be involved in the operation" and "will no longer be in the immediate area" in northern Syria.
The statement on Sunday also said Turkey will take custody of foreign fighters captured in the US-led campaign against IS who have been held by the Kurdish forces.
The Kurds have custody of thousands of captured IS militants.
They include about 2,500 highly dangerous foreign fighters from Europe and elsewhere - their native countries have been reluctant to take them back - and about 10,000 captured fighters from Syria and Iraq.
Kurdish officials have expressed concerns of a possible breakout by IS prisoners in case of fighting in the area.
Asked about the White House comments, Mr Erdogan said that both Turkey and the US were working separately to see "what steps can be taken" so that foreign fighters in prison can be repatriated.
Mr Erdogan has threatened for months to launch the military operation across the border.
He views the Syria Kurdish forces as terrorists and a threat to his country as Ankara has struggled with a Kurdish insurgency within Turkey.
Sunday 5th of April 2020