U.S. officials say the Pentagon will begin deploying as many as 1,500 active duty troops to help secure the southern border in the coming days.

Troops have assisted at the border before and will be limited to support roles unless the administration invokes the Insurrection Act.

The U.S. military will send 1,500 additional active-duty troops to the border with Mexico, the White House said on Wednesday, just two days after President Donald Trump signed an executive order on immigration.

"It's unprecedented," said Ciudad Juarez municipal official Enrique Licon as workers unloaded long metal bracings from tractor trailers parked in the large empty lot yards from the Rio Grande in order to build a tent city for deportees from the United States.

The order will deploy 1,500 troops to build physical barriers, but they will not be used for law enforcement, a military official says.