If necessary, the soldiers of the additional forces can move around the country and can leave the territory of Syria from time to time, according to the CNN broadcaster.
The US officials did not disclose how much time the withdrawal would take. They also did not provide information on whether it had already started.
The news about the reinforcements comes after an explosion in the Kurdish-held city of Manbij claimed lives of at least four US troops.
* Daesh (ISIL/ISIS/IS/Islamic State) is a terrorist organisation banned in Russia