President Donald Trump has threatened to destroy Turkey’s economy if the country goes “off limits” following his surprise decision to pull US forces out of north-eastern Syria.
US military vehicles were filmed moving away from the border on Monday
In a series of angry tweets, Mr Trump defended his move, which could open the way for Turkey to launch an attack on Kurdish fighters across the border.
The withdrawal was heavily criticised even by Mr Trump’s Republican allies.
Kurdish forces were key US allies in defeating Islamic State (IS) in Syria.
But Turkey regards the Kurdish militias, which dominate the US-allied Syrian Democratic Forces (SDF), as terrorists.
The US has some 1,000 troops across Syria, but only about two dozen had been pulled out from the border area, according to a senior state department official.
What is President Trump’s position?
Mr Trump initially tweeted on Monday he had been elected on “getting out of these ridiculous endless wars” and that “Turkey, Europe, Syria, Iran, Iraq, Russia and the Kurds will now have to figure the situation out”.
This had followed a phone call on Sunday with Turkish President Recep Tayyip Erdogan, after which the White House said Turkey would be “moving forward with its long-planned operation into northern Syria” and US forces would “no longer be in the immediate area”.
Following accusations from US Kurdish allies they had been “stabbed in the back” and criticism from across the US political spectrum, Mr Trump sent out more tweets later on Monday, warning Turkey not to take advantage of his decision, saying he could “destroy and obliterate” its economy.
Last year, the US raised tariffs on some Turkish products and imposed sanctions on top officials as relations between the two Nato countries worsened over a number of issues.
Later when expanding on his “off limits” tweet, Mr Trump said Turkey should “not do anything outside of what we would think is humane”.
He also said there would be “big trouble” if “any of our people get hurt”.
In a statement, Pentagon spokesman Jonathan Hoffman said “the Department of Defense made clear to Turkey – as did the president – that we do not endorse a Turkish operation in Northern Syria”.
What does Turkey want to do in Syria?
At the recent UN General Assembly, Mr Erdogan produced a map showing a 480km (300 mile) long and 30km deep “safe zone” that he wants Turkey to control along its border with Syria.
This would resettle up to two million of the more than 3.6 million Syrian refugees currently living in Turkey.
On Monday, Turkey’s defence ministry said that “all preparations for the operation have been completed,” adding the establishment of such a zone was “essential” for Syrians and for peace in the region.
But Turkey has also repeatedly threatened to attack Kurdish fighters across the border in north-eastern Syria.
Turkey considers the Kurdish YPG militia – the dominant force in the SDF – an extension of the banned Kurdistan Workers’ Party, which has fought for Kurdish autonomy in Turkey for three decades.
Separately on Tuesday, Iran said it opposed any Turkish military action in Syria.