Border security is a key priority for President Donald Trump, who declared a national emergency at the US frontier with Mexico on his first day in office.

"Approximately 2,400 soldiers from elements of the 2nd Stryker Brigade Combat Team (SBCT), 4th Infantry Division" will be sent to the border, along with "approximately 500 soldiers from the 3rd Combat Aviation Brigade," NORTHCOM said in a statement.

"Tasks carried out by 2nd SBCT will include detection and monitoring; administrative support; transportation support; warehousing and logistic support; vehicle maintenance; and engineering support. Personnel will not conduct or be involved in interdiction or deportation operations," it said.

Troops from the aviation unit will meanwhile "assist in the movement of personnel, equipment, and supplies; and provide aerial medical evacuation capabilities," NORTHCOM said.

"These deployments will bring additional agility and capability to further efforts to stop the flow of illegal migrancy and drugs at the southern border," its commander General Gregory Guillot said.

The Trump administration has launched what it cast as a major effort to combat illegal migration that has included immigration raids, arrests and deportations, including via the US naval base at Guantanamo Bay in Cuba.

Trump unveiled a surprise plan last month to hold up to 30,000 migrants at the base -- a facility notorious for abuses against terror suspects detained after the September 11, 2001 attacks -- and US forces have detained dozens of people there in recent weeks, many of whom have since been deported.