Houston, Texas - Donald Trump's promised war on drug cartels will stop Mexico from becoming a "narco state," Vice President JD Vance said Wednesday, as he hinted that Washington remained ready to take military action against the gangs.

Speaking at the US southern border, Vance said the administration's focus on stamping out illegal immigration and on designating gangs as terrorist organizations was aimed primarily at stemming the flow of drugs into the US.

But, he said, "I actually think he's doing a huge favor to the people of Mexico, because if they don't get control of these cartels, the people of Mexico are going to wake up in a narco state where the cartels have more power than their own government."

Vance's comments came after Trump used a joint session of Congress to rail against what he called the "open border" policies of former president Joe Biden, and issued a blood-curdling warning over criminal gangs operating in Mexico.

Politicians RFK Jr's solution to measles outbreak has medical experts tearing their hair out

"The territory to the immediate south of our border is now dominated entirely by criminal cartels that murder, rape, torture and exercise total control," Trump told Congress on Tuesday.

"The cartels are waging war in America, and it's time for America to wage war on the cartels."

Vance, the most senior figure in Trump's administration to visit the border, said there was no talk of US military forces crossing into Mexico to tackle the gangs, which he said were now classified alongside the so-called Islamic State group as "terrorists."

But he left the door open.

"I'm not going to make any announcements about any invasions of Mexico here today," he said.

Politicians Marco Rubio gets flustered playing defense for Trump's contentious Zelensky meeting

"The President has a megaphone, and of course, he'll speak to... these issues as he feels necessary."

The administration would rather that Mexico dealt with the issue, he said.

"We want the Mexican government to help itself, but also in the process, to help the American people. It's going to destabilize the entire country of Mexico, the entire government, if they don't take it more seriously," Vance said.

"We're hopeful that they will, and if they don't, then of course, we'll figure out what to do from there."

This comes after Secretary of Defense Pete Hegseth last week authorized the deployment of 3,000 US troops to the southern border.