United Nations says it was "preparing for the worst" in northeast Syria

The United Nations said Monday it was "preparing for the worst" in northeast Syria after the United States said it would step aside to allow for Turkish military operations in the area.

"We don't know what is going to happen... we are preparing for the worst," UN regional humanitarian coordinator for Syria, Panos Moumtzis, said in Geneva, stressing that 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.

But he made clear his office did not have advance warning about the US decision that effectively abandons the Kurds, who were Washington's main ally in the long battle against the so-called Islamic State group.

Moumtzis said the UN's priorities were to ensure that any prospective Turkish offensive not result in new displacements, that humanitarian access remain unhindered and that no restrictions be put in place on freedom of movement.

The UN has a contingency plan to address additional civilian suffering, but "hopes that will not be used," Moumtzis said.

Turkey has sent reinforcements to the border in recent weeks, and President Recep Tayyip Erdogan said Monday the long-threatened offensive could "come any night without warning".

His comments came after Foreign Minister Mevlut Cavusoglu said on Twitter that Turkey was "determined to ensure our country's existence and security by clearing terrorists from this region".

He was referring to the SDF, or Syrian Democratic Forces, which have ties to Kurdish militants inside Turkey and which Ankara considers a terrorist organisation.