US troops on Monday began pulling out of positions along the border in northeast Syria ahead of an expected invasion by Turkey, according to US-allied Kurdish forces.

The Kurdish militia in Syria said a Turkish attack could reverse gains made against Islamic State.

The development comes hours after the White House announced that “Turkey will soon be moving forward with its long-planned operation into Northern Syria.”

“The United States Armed Forces will not support or be involved in the operation,” a statement read. “Turkey will now be responsible for all ISIS fighters in the area captured over the past two years in the wake of the defeat of the territorial ‘Caliphate’ by the United States.”

Meanwhile, a senior Turkish official told Reuters that his country is highly likely to wait until American forces have withdrawn before launching an offensive to avoid “any accident” — adding that it will take US troops about a week to clear the planned area of operations.

The Syrian Kurdish fighters also accused Washington of failing to abide by its commitments to its key allies in the fight against the terror group, a major shift in US policy.

There was no immediate confirmation from the White House on Monday of movements by US troops in northern Syria.

Turkish President Recep Tayyip Erdogan also said the US forces have started withdrawing from positions — and a video posted by a Kurdish news outlet showed a convoy of American armored vehicles apparently pulling out of the border area of Tal Abyad.

Erdogan didn’t elaborate on the planned Turkish invasion but said Ankara was determined to halt what it perceives as threats from the Syrian Kurdish fighters, whom Turkey considers a terrorist group.

US lawmakers on both side of the aisle have warned that allowing the Turkish attack could lead to a massacre of the Kurds and send a troubling message to US allies across the world.

The Syrian Democratic Forces — as the Kurdish-led force is known — said the US pullout began first from areas along the Syria-Turkey border.

“The American forces did not abide by their commitments and withdrew their forces along the border with Turkey,” the SDF said in a statement. “Turkey now is preparing to invade northern and eastern parts of Syria.”

It added: “The Turkish military operation in northern and eastern Syria will have a huge negative effect on our war against” ISIS.

In an agreement between Ankara and Washington, joint forces had been patrolling a security zone that covers about 80 miles along the border between the towns of Tal Abyad and Ras al-Ayn.

Turkey and the US disagreed over the depth of the zone, with Ankara seeking to also have its troops monitor a stretch of territory between 19 and 25 miles. Despite the agreement, Erdogan had continued to threaten an assault.

The Kurdish-led fighters have been the main US-backed force in Syria in the fight against ISIS, and in March, the group captured the last bit of territory held by the jihadists, marking the end of the so-called caliphate that was declared by ISIS leader Abu Bakr al-Baghdadi in 2014.

“We will not hesitate for a moment in defending our people” against Turkish troops, the Syrian Kurdish force said, adding that it has lost 11,000 fighters in the war against the terror group in Syria.

A Turkish attack would lead to a resurgence of ISIS, whose sleeper cells are already plotting to break free some 12,000 extremists held by Syrian Kurdish fighters in northeastern Syria in a “threat to local & international security,” it said.

With Post wires