In his first trip as Pentagon chief, Hegseth met with US troops -- who have been surged to the border region under Trump -- and then traveled to the frontier itself.

"This is a new era at the southern border, a new era of determination, a new era of cooperation. And at the Defense Department, we are proud to be a part of it," Hegseth said in televised remarks.

"We are going to get control of this border," he vowed.

Trump has ordered 1,500 additional military personnel to the border and his administration has carried out highly publicized immigration raids and arrests. Some migrants have additionally been deported using military aircraft.

Border security is a key priority for the president, who declared a national emergency at the US frontier with Mexico on his first day in office and also designated drug cartels as terrorist organizations.

"To the cartels, all options are on the table," Hegseth said Monday, without providing further details.

He 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 last week ordered the preparation of a 30,000-person facility to hold migrants at the military base, which is primarily known as a detention center for suspects accused of terrorism-related offenses.

US Southern Command said Monday that 150 additional troops had been deployed to the base over the weekend to support "illegal alien holding operations."