Turkey said Tuesday it was ready for an offensive against Kurdish militants in northern Syria despite mixed signals from US President Donald Trump over whether he had approved the operation.
The United States pulled back 50 to 100 "special operators" from Syria's northern frontier on Monday, where they had served as a buffer preventing a long-planned assault by the Turkish military against Kurdish forces.
Trump's surprise move drew heavy criticism from top Republicans that he was abandoning the Kurds, who were crucial in the years-long campaign to defeat Islamic State.
But he later appeared to backpedal, warning Turkey that he would "obliterate" the country's economy if it went too far -- without explaining what that meant.
"I have told Turkey that if they do anything outside of what we would think is humane... they could suffer the wrath of an extremely decimated economy," he said.
Ankara brushed aside the threat on Tuesday, with Vice-President Fuat Oktay saying: "Turkey is not a country that will act according to threats."
Turkey has always pushed hard against Washington's 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".
The Syrian government said it was an opportunity to welcome the country's Kurds back into its fold.
The Kurds have been "tossed aside" by Washington, Syrian Deputy Foreign Minister Faisal Mekdad told the pro-government Al-Watan newspaper.
"We will defend all Syrian territory, and we will not accept any occupation of Syrian land," he added.
- US allies abandoned? -
Even Trump's allies accused him of turning his back on the Kurds, who lead the Syrian Democratic Forces (SDF) and say they lost some 11,000 fighters as the main frontline force against the Islamic State group.
A senior US official denied Trump had given a "green light" to a Turkish invasion, which has also raised concerns over the fate of thousands of Islamic State prisoners held in Kurdish detention centres.
Trump himself put the emphasis on ending the US military presence in the region.
"We want to bring our troops back home from these endless wars and we're like a police force. We're not fighting. We're policing," he tweeted on Monday.
But senior Republicans criticised the decision, with even staunch ally Mitch McConnell, the Senate Majority leader, saying: "A precipitous withdrawal of US forces from Syria would only benefit Russia, Iran, and the Assad regime."
Iran, a key backer of the Syrian government, also said on Tuesday it opposed any military action by Turkey.
In a call to Ankara, Foreign Minister Mohammad Javad Zarif "urged respect for Syria's territorial integrity".
- 'Safe zone' -
Ankara says it wants to establish a "safe zone" on the Syrian side of the border where it could send back some of the 3.6 million refugees from the eight-year civil war.
President Recep Tayyip Erdogan said Monday that the operation into Syria could "come any night without warning," while Kurds in the area girded for fighting.
Kurds argue that Ankara's goal is to dilute their dominance in the region with an influx of mostly Sunni Arab refugees now living in southwestern Turkey.
Trump's announcement appeared to have caught many US officials by surprise, and they spent Monday seeking to discourage Ankara from acting.
Pentagon spokesman Jonathan Hoffman warned Turkey of destabilizing blowback to the region if it invades.
"The Department of Defense made clear to Turkey -- as did the president -- that we do not endorse a Turkish operation in Northern Syria," he said.
SDF spokesman Mustefa Bali said Washington's decision "is about to ruin the trust and cooperation between the SDF and US."
A Turkish attack raised the specter of some 10,000 Islamic State fighters currently held by the SDF being let loose if SDF soldiers have to battle Turkish troops.
Around 2,000 of them are IS "foreign fighters", and Trump assailed US allies in Europe for not taking back their nationals.
If they escape or are released, they could reconstitute the Islamic State, less than one year after it was defeated and its "caliphate" disintegrated.
Trump declared that it would be the responsibility of Turkey and other countries to deal with the IS prisoners.
"Turkey, Europe, Syria, Iran, Iraq, Russia and the Kurds will now have to figure the situation out, and what they want to do with the captured ISIS fighters in their 'neighborhood,'" he said, using another acronym for the jihadists.