Turkish President Tayyip Erdogan stated on Wednesday that Turkey will launch the military operation in a days, targeting a border region which is held by the YPG Kurdish militia.

The announcement prompted a sharp rebuke from the Pentagon, which said any unilateral military action into northeast Syria would be unacceptable.

The spokesman for the National Army, a Turkish-backed rebel force aimed at unifying disparate factions in northwest Syria, said on Thursday that there was no set date for the operation, which will start from both Syrian and Turkish territory.

“The battle will be launched simultaneously from several fronts,” Major Youssef Hamoud told Reuters.

“It will be in Manbij and Tel Abyad and Ras al-Ayn,” he said, referring to towns about 200 km apart near Syria’s northern border.

Hamoud said the operation from Turkey may begin a few days before the move from within Syria.

Commander Sean Robertson, a Pentagon spokesman, said in a statement that unilateral military action into northeast Syria by any party would be of grave concern, “particularly as U.S. personnel may be present or in the vicinity.”

Reporter’s code: 50101