U.S. officials say active duty military troops are arriving in El Paso, Texas, and in San Diego on Thursday evening

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

Acting Defense Secretary Robert Salesses said the troops will fly helicopters to assist Border Patrol agents and help in the construction of barriers.

The Pentagon said Wednesday it has begun deploying 1,500 active-duty troops to the southern border, putting in motion plans President Trump laid out in executive orders shortly after he took office to crack down on immigration.