President Donald Trump has threatened to destroy Turkey's economy if Turkey goes "off limits" after his surprise decision to pull US forces out of north-eastern Syria.
In a series of angry tweets, Mr Trump defended the move that 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 the Islamic State in Syria.
The US has some 1,000 troops across Syria and about two dozen had been pulled out from the border area, according to a senior state department official.
The withdrawal was described by the main Kurdish-led group as a "stab in the back", and critics say it could facilitate an IS resurgence and leave Kurdish forces at risk of being attacked by Turkey, which regards them as terrorists.
But Mr Trump warned Turkey not to take advantage of his decision - which goes against the advice of senior officials in the Pentagon and state department - saying he could "destroy and obliterate" its economy.
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!). They must, with Europe and others, watch over...— Donald J. Trump (@realDonaldTrump)
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.
Turkish President Recep Tayyip Erdogan has said his aim is to combat Kurdish fighters in the border area and set up a "safe zone" for up to two million of the more than 3.6 million Syrian refugees currently living in Turkey.
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".
Earlier, Mr Trump said it was time "to get out of these ridiculous Endless Wars, many of them tribal" and that "Turkey, Europe, Syria, Iran, Iraq, Russia and the Kurds will now have to figure the situation out".
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