The Pentagon is sending 1,500 active duty troops to help secure the southern US border with Mexico

The United States Department of Defence has begun the process of deploying more manpower to secure the country’s southern border.

Some 1,500 active duty troops are being sent down after plans were put in motion by the newly sworn-in US President Donald Trump.

The 47th US president got to work quickly after reoccupying the Oval Office on Monday. On Inauguration Day, Trump signed a slew of executive orders, signalling a sharp U-turn from the Biden administration. Among the orders were plans to crack down on immigration.

Acting Defence Secretary Robert Salesses said the troops will fly helicopters to assist Border Patrol agents on the ground, as well as help in the construction of barriers. The Pentagon will also provide more military aircraft for Department of Homeland Security deportation flights, for more than 5,000 detained immigrants.

Salesses says the number of troops and their missions may soon change, adding that “this is just the beginning”.

“In short order, the department will develop and execute additional missions in cooperation with DHS, federal agencies, and state partners to address the full range of threats outlined by the President at our nation’s borders," Salesses said.

Defence officials say the department is prepared to offer even more troops if requested and necessary. They’ve noted that up to 2,000 more Marines can be made available and deployed to the southern border with Mexico.

Officials added that there were no plans for now for the deployed troops to do law enforcement, but that can change based on decisions and orders from the White House.

Troops are prohibited by law from doing law enforcement duties under the Posse Comitatus Act, passed in 1878. Trump does however have the ability to invoke the Insurrection Act of 1807, which would allow troops to be used in civilian law enforcement.

Trump has instructed the incoming Defence Secretary Pete Hegseth, and Homeland Security chief to report back within three-months if it needs to be invoked. The last time the act was invoked was back in 1992 by President George H.W. Bush to quell Los Angeles rioting after policemen charged with beating Rodney King were acquitted.

The active duty forces will join roughly 2,500 US National Guard and Reserve forces already present at the border. Until this deployment, no active duty troops were working along the 2,000 mile (3220 km) long border.

There are currently about 20,000 Border Patrol agents in active service. While most are located in the south, they’re also responsible for protecting the northern border with Canada. Agents there are tasked with identifying drug smugglers, while staff in the south are mainly on the lookout for illegal migrants.