US President Donald Trump vowed "very serious retaliation" on Saturday after an ISIS gunman ambushed and killed two US soldiers and a civilian interpreter in Syria, calling the deadly strike as an assault on both the US and the war-torn Syria.

The order, handed down by U.S. District Court Judge Charles Breyer, is a blow to the Trump administration, and comes six months after the president in June deployed thousands of federalized National Guard troops to the city in response to a wave of immigration protests.

U.S. District Judge Charles Breyer said the Trump administration has made "clear that the only check" it wants "is a blank one."

The judge has ordered control of the the troops, which were deployed in June, to be returned to California's governor.