ISTANBUL  - The Turkish military carried out strikes targeting the Syrian-Iraqi border overnight to prevent Kurdish forces using the route to reinforce northeast Syria, as Ankara prepares to launch an offensive there, two Turkish officials told Reuters on Tuesday.

Turkey says it has finalised preparations for a military push into northeast Syria, after the United States began pulling back troops from the Turkey-Syria frontier area in a move widely criticised in Washington as a betrayal of America’s allies.

The US move will leave Kurdish-led forces long allied to Washington vulnerable to attack 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.

Giving details of the overnight strike, a security official said one of the main goals was to cut off the transit route between Iraq and Syria “before the operation in Syria”. “In this way, the group’s transit to Syria and support lines, including ammunition, are shut off,” the official said.

It was not clear what damage was caused or whether there were casualties. Details of the strike were hazy. One official described them as an air strike, while the other said the site was made “unusable through various means”.

President Donald Trump meanwhile denied the Kurds had been abandoned by the US pullback, praising Turkey as a trade partner and NATO ally in a softening of his tone hours after threatening Ankara’s economy if it acted “off limits” in Syria.

Ankara says it has finalised preparations for a military push into northeast Syria

Signalling a further potential shift in the region’s power balance, the Kurdish-led forces said they might start talks with Damascus and Russia to fill a security vacuum in the event of a full US withdrawal from the Turkish border area.

Turkey sought to underscore its determination to act. “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.

But a Reuters witness saw no sign of military activity near the Turkish border town of Akcakale, across from Syria’s Tel Abyad. Howitzers were placed behind earth embankments on Turkey’s side of the border, pointed towards Syria. Some 60 km (40 miles) to the west, multiple launch rocket systems mounted on two trucks were deployed behind earth embankments near Suruc, opposite the Syrian border town of Kobani. Artillery was also stationed in the area, and soldiers wandered around a nearby military camp.

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 on Monday 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 his 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, reiterated on Tuesday in slightly modified form, met an angry response in Turkey, including from opposition party politicians such as Iyi Party leader Meral Aksener. “Threatening Turkey’s economy is a diplomatic catastrophe,” she told her party’s lawmakers in a speech in parliament. “The best response to this insolence is to go into the east of the Euphrates and break the terror corridor.”

But on Tuesday, Trump tweeted: “So many people conveniently forget that Turkey is a big trading partner of the United States ... They have been good to deal with.”

As for the Kurds, he said their “wonderful fighters” continued to receive US help with finance and weapons. The Kurdish-led forces, who have been the most effective US partners in fighting Islamic State in Syria, have denounced the major US policy shift as “stab in the back”.

Mustafa Bali of 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”.

Syrian Kurdish official Badran Jia Kurd said Kurdish-led authorities in northern Syria may open talks with Damascus and Russia US forces fully withdrew from the Turkish border area. His comments reflect the predicament of Kurdish-led forces in northern Syria after the partial withdrawal of US troops who have effectively shielded the area from Turkish attack.

 “At that time we may hold talks with Damascus or the Russian side to fill the void or block the Turkish attack, so this may develop and there could be meetings and contacts in case of a vacuum,” he told Reuters. Syria said it would defend itself against any Turkish assault. “We will not accept any occupation of any land or grain of soil,” deputy foreign minister Faisal Mekdad told al-Watan newspaper. Damascus was not able to prevent Turkey taking control of a swathe of northwestern Syria earlier in the war.

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.