US forces in Syria started pulling back Monday (October 7th) from Turkish border areas, AFP reported.
The withdrawal from key positions along Syria's northern border came after the White House said it would step aside to allow for a Turkish operation President Recep Tayyip Erdogan has said could come at any moment.
The Pentagon warned however that the US does not endorse a threatened Turkish invasion of northern Syria, saying it risked destabilising the region.
"We will work with our other NATO allies and coalition partners to reiterate to Turkey the possible destabilising consequences of potential actions to Turkey, the region, and beyond," Pentagon spokesman Jonathan Hoffman said.
The Syrian Democratic Forces (SDF), a key US partner in the battle against the "Islamic State of Iraq and Syria" (ISIS) that controls much of north-eastern Syria, on Monday said "US forces withdrew from the border areas with Turkey".
The Syrian Observatory for Human Rights confirmed that US forces had pulled back from key positions in Ras al-Ain and Tal Abyad.
A Kurdish official also said US forces had started withdrawing from the border, making way for a Turkish invasion, the scope of which remains to be seen.
Turkey has sent reinforcements to the border in recent weeks, and Erdogan said Monday in televised remarks the long-threatened offensive could "come any night without warning".
"The US Armed Forces will not support or be involved in the operation, and US forces, having defeated the ISIS territorial 'Caliphate,' will no longer be in the immediate area," the White House said.
President Donald Trump on Monday justified his decision to withdraw US troops from Turkey's border with Syria, saying the region would have to "figure the situation out" and that the US needed to get out of "ridiculous Endless Wars".
But top Trump ally US Senator Lindsey Graham, chairman of the Senate Judiciary Committee, said Monday he would be calling on Congress to reverse the president's decision, expecting this move to gain "strong bipartisan support".
UN 'in contact with all sides'
Ankara says it wants to urgently establish a "safe zone" on the other side of the border, where it plans to repatriate some of the 3.6 million Syrian refugees who currently reside in Turkey.
But the Kurds claim Turkey's goal is to weaken the Kurdish presence in the region by modifying the demographics of the area with the return of mostly Sunni Arab refugees.
The SDF warned of the risks that a Turkish invasion would carry for the region, and vowed to resist any Turkish attack.
"As the Syrian Democratic Forces, we are determined to defend our land at all costs," it said in a statement posted on social media.
In a Monday statement, the SDF said a Turkish offensive would reverse the military gains achieved against ISIS at great human cost and allow for the extremist group's surviving leaders to come out of hiding.
The UN said Monday it was "preparing for the worst" in north-east Syria.
UN regional humanitarian co-ordinator for Syria Panos Moumtzis said there were "a lot of unanswered questions" about the consequences of the operation.
Moumtzis added that the UN was "in contact with all sides" on the ground.
The EU also warned that a threatened Turkish offensive would harm civilians and cause "massive displacement" of people.