The United States has no timeline for the withdrawal of American troops from Syria but does not plan to stay indefinitely, a senior State Department official said on Friday, sending a strong signal that U.S. forces could stay until the fight against Islamic State militants is over.

U.S.-backed forces are still retaking territory from Islamic State in Syria, Pentagon officials said on Friday, two weeks after Washington said it would withdraw the roughly 2,000 U.S. troops in the country. President Donald Trump said at the time that the troops had succeeded in their mission and were no longer needed there.

The administration's abrupt announcement last month, which took officials in Washington and allies by surprise, contributed to Jim Mattis' decision to resign as U.S. defense secretary and prompted concern that Islamic State could stage a comeback.