"The execute order for Syria has been signed," the spokesperson told AFP, without providing further details.

US President Donald Trump has declared the jihadist group "largely defeated," and made the surprise decision to bring US forces home -- a move that many US politicians and international allies fear is premature and would further destabilize the already devastated region.

The decision -- which was followed by another to make a significant cut to the number of American troops in Afghanistan -- has prompted the resignation of Defense Secretary Jim Mattis and US envoy to the international anti-IS coalition Brett McGurk.