Turkey said Tuesday it was ready for an offensive into northern Syria, while President Donald Trump insisted the United States had not abandoned its Kurdish allies who would be targeted in the assault.
Trump has blown hot and cold since a surprise announcement on Sunday that Washington was pulling back 50 to 100 "special operators" from Syria's northern frontier.
The troops had served as a buffer preventing a long-planned attack by the Turkish military against Kurdish forces, who were crucial in the years-long campaign to defeat the Islamic State group but are viewed as "terrorists" by Ankara.
After appearing to give a green light to the Turkish invasion on Sunday, Trump later threatened to "obliterate" Turkey's economy if it went too far.
"Any unforced or unnecessary fighting by Turkey will be devastating to their economy and to their very fragile currency," he tweeted.
But he also gave a warm account of Turkey in other tweets and announced that President Recep Tayyip Erdogan would visit Washington on November 13. "So many people conveniently forget that Turkey is a big trading partner of the United States," he said.
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Ankara had already brushed aside Trump's warnings, with Vice-President Fuat Oktay saying: "Turkey is not a country that will act according to threats." Turkey has always pushed hard against US support for Kurdish forces in Syria due to their links with the outlawed Kurdistan Workers' Party (PKK) which has fought a bloody insurgency against the Turkish state since 1984.
Its defence ministry tweeted that preparations for an offensive in northern Syria have been "completed".
Meanwhile, the Syrian government has welcomed the upheaval, spying an opportunity to bring the country's Kurds back into its fold. The Kurds have been "tossed aside" by Washington, Syrian Deputy Foreign Minister
Trump rejected that interpretation, tweeting: "We may be in the process of leaving Syria, but in no way have we Abandoned the Kurds, who are special people and wonderful fighters."