Istanbul: Turkey said on Tuesday it had completed preparations for a military operation in northeast Syria after the United States began pulling back troops, opening the way for a Turkish attack on Kurdish-led forces long allied to Washington.
But US President Donald Trump warned he would "obliterate" the NATO ally's economy if it took action in Syria that he considered "off limits" following his decision on Sunday to pull 50 American special forces troops from the border region.
The US move will leave its Kurdish-led partner forces in Syria vulnerable to an incursion by the Turkish Armed Forces (TSK), which brands them terrorists because of their links to Kurdish militants who have waged a long insurgency in Turkey.
"The TSK will never tolerate the establishment of a terror corridor on our borders. All preparations for the operation have been completed," the Turkish Defence Ministry said on Twitter early on Tuesday.
"It is essential to establish a safe zone/peace corridor to contribute to our region's peace and stability, and for Syrians to achieve a safe life," it said.
A Reuters witness said there was no sign of military activity on Tuesday near the Turkish border town of Akcakale, across from Syria's Tel Abyad. Howitzers were positioned behind earth embankments on the Turkish side of the border, pointed towards Syria.
US forces evacuated two observation posts at Tel Abyad and Ras al Ain on Monday, a US official said.
Trump's warning on Turkey's economy appeared aimed at placating critics who accused him of abandoning the Syrian Kurds by pulling out US forces. The decision drew criticism from Democrats and a rebuke from some of Trump's fellow Republicans in Congress, including Senate Majority Leader Mitch McConnell.
"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!)" Trump tweeted.
His remarks met an angry response in Turkey, including from opposition party politicians such as Iyi Party leader Meral Aksener who said it was a day to put aside domestic politics.
"Threatening Turkey's economy is a diplomatic catastrophe," she told her party's lawmakers in a speech in parliament. "Today there is only one party and that is our red (Turkish) flag."
"The best response to this insolence is to go into the east of the Euphrates and break the terror corridor," she added.
The Kurdish-led forces, who have been Washington's most capable partners in fighting Islamic State in Syria, have denounced the major shift in US policy as "stab in the back".
Mustafa Bali, an official with the Kurdish-led Syrian Democratic Forces (SDF) said the continued Turkish military buildup on the border, together with information about further mobilisation of Turkey-backed Syrian rebels, indicated that "an attack is imminent and we expect it soon".
"Naturally our preparations are along the length of the border with Turkey and our forces are in a state of readiness," Bali told Reuters.
The United States expects Turkey to take responsibility for captive Islamic State fighters in northeastern Syria if Ankara's planned incursion seizes areas where the detained militants are held, a senior State Department official said.
The captives are held in SDF facilities south of a safe zone initially proposed by Turkey.
Turkish Foreign Ministry spokesman Hami Aksoy said overnight it was Turkey's fundamental right to take necessary measures for its national security against terrorism threats from Syria.
"Turkey is determined to clear terrorists from the east of the Euphrates and protect its own security and survival while implementing a secure zone in order to achieve peace and stability," Aksoy said in a written statement.
Russia, Syrian President Bashar al-Assad's strongest foreign ally, said it was not told in advance by the United States or Turkey about any agreements they had about plans to pull US troops from the northeast, adding it was watching the situation very closely.
Iran, another Assad ally, voiced opposition to any Turkish military operation in Syria. "Such an action will not only not end Turkey's security concerns but will lead to widespread material and human damage," Iran's foreign ministry said.
President Tayyip Erdogan has said Turkey plans to resettle two million refugees in northern Syria and Turkish media has said the draft resettlement plan involves a 151 billion lira ($26 billion) construction project. Turkey hosts 3.6 million Syrian refugees.
The Trump administration official, briefing reporters on a conference call, said 50 US troops in the region that Turkey has targeted would be redeployed elsewhere in Syria "where they aren't in the crossfire." The United States has about 1,000 troops in Syria.
Ties between Ankara and Washington have long been tense over a range of issues including Syria policy and Turkey's purchase of a Russian missile defence system.