WASHINGTON—The White House indicated that U.S. forces will withdraw from northern Syria in advance of an expected incursion of Turkish forces in the region that could spark fighting with American-backed Kurds, in what officials believe could be the end of the fight against Islamic State there.

“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, and United States forces, having defeated the ISIS territorial ’Caliphate,’ will no longer be in the immediate area,” White House press secretary Stephanie Grisham said in a statement.

The statement, released just before 11 p.m. in Washington, followed an earlier phone call Sunday between President Trump and Turkish President Recep Tayyip Erdogan.

The White House statement marks a change in policy for American dealings with Turkey, as well as a tactical shift if Washington abandons a key partner—the Kurds—in the fight against Islamic State.

Turkey’s incursion might mean the complete withdrawal of American forces from Syria, a U.S. official said early Monday.