Active duty troops deploying to U.S.-Mexico border, White House says.

WASHINGTON – The Pentagon will soon deploy as many as 1,500 additional active duty forces to the country’s southern border, the White House said Wednesday, following through on an executive order President Donald Trump signed shortly after taking office.

White House press secretary Karoline Leavitt said the deployment will help carry out Trump's promise of a border crackdown. The move comes in the wake of several border-related executive actions Trump has enacted since his Monday inauguration including declaring a national emergency at the U.S.-Mexico border.

A senior defense official told reporters on condition of anonymity on Wednesday that the troops had already begun to deploy to the border, and would begin operating there within 24 to 48 hours.

The 1,500 troops include 1,000 Army personnel and 500 Marines, according to the official. The Marines were assigned to respond to wildfires in California, and will now be reassigned to the border, the official said.

The troops will place physical barriers, provide situational awareness and intelligence, and work with Customs and Border Protection on movement and staging, according to the official. Four military aircraft – two C-17 and two C-130 planes – will be deployed in San Diego and El Paso to carry out deportations and move personnel.

The troops would not perform law enforcement duties. The decision to arm them would be left up to the commander for U.S. Northern Command, according to the official.

A senior defense official said the number of troops could expand by thousands more – the White House had not yet given the Defense Department a number.

Approximately 2,500 members of the National Guard and Army Reserve are already at the border assisting U.S. Customs and Border Protection with logistics and other support duties, a Pentagon spokesperson told USA Today. The new tranche of troops will support that ongoing mission, according to a defense official who was not authorized to speak publicly.

Active duty troops were last ordered to the border by former President Joe Biden’s administration, and Trump did the same during his first term.

Learn more: Trump pledges to send military to border, brands cartels terrorists. Here's what we know.

Unless the administration invokes the Insurrection Act, active duty troops can't assist in apprehensions and will be limited to support roles as they have in the past.

Davis Winkie's role covering nuclear threats and national security at USA TODAY is funded by a grant from Outrider Foundation. Outrider Foundation does not provide editorial input. You can reach Davis via email at [email protected] or via the Signal encrypted messaging app at 770-539-3257.

(This story has been updated to add new information.)

This article originally appeared on USA TODAY: Active duty troops heading to US-Mexico border