The U.S. will withdraw about 600 troops from Syria, leaving fewer than 1,000 to work with Kurdish allies to counter the Islamic State group, a U.S. official said Thursday. The official spoke on the condition of anonymity to discuss details not yet announced publicly.

The U.S. military has about 2,000 U.S. troops in Syria across a number of bases, mostly in the northeast. The troops are working with local forces to prevent a resurgence of Islamic State, which in 2014 seized large swathes of Iraq and Syria but was later pushed back.

The departure would return force levels to where they had been for years, after the U.S. and its allies waged a multiyear campaign to defeat ISIS.