Turkish President Recep Tayyip Erdogan says American troops have started withdrawing from positions in northern Syria.

Erdogan spoke on Monday, hours after the White House said that U.S. forces in northeast Syria will move aside and clear the way for an expected Turkish incursion. The announcement cast uncertainty on the fate of the Kurdish fighters allied with the U.S. against against the Islamic State group.

Turkey has threatened for months to launch a military operation to drive away Syrian Kurdish fighters from a border region east of the Euphrates River.