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," US Northern Command (NORTHCOM) said in a statement.

The Stryker unit "will not conduct or be involved in interdiction or deportation operations," it said, but rather will assist in detection and monitoring, administrative duties and transportation and engineering support, among other tasks.

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.

- Trump says 'invasion' is over -

The Trump administration has launched what it cast as a major effort to combat illegal migration that has included immigration raids, arrests and deportations.

Trump on Saturday hailed his administration's border security efforts, posting on his Truth Social platform that "the Invasion of our Country is OVER."

"Thanks to the Trump Administration Policies, the Border is CLOSED to all Illegal Immigrants. Anyone who tries to illegally enter the U.S.A. will face significant criminal penalties and immediate deportation," the president wrote.

Pentagon chief Pete Hegseth visited the southern frontier at the beginning of last month, vowing that "we are going to get control of this border."

He warned drug cartels that "all options are on the table," after Trump signed an executive order in January that said they "constitute a national security threat beyond that posed by traditional organized crime."

Hegseth also said that "any assets necessary" from the Defense Department will be used to support "the expulsion and detention of those in our country illegally," including the US 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 held dozens of people there in recent weeks, many of whom have since been deported.