Donald Trump has said he will deploy members of the military to the US border with Mexico until his long-promised wall is built.

“Until we can have a wall and proper security, we’re going to be guarding our border with the military,” he said at a press conference with Baltic leaders. ”It’s a big step.”

He said: “We really haven’t done that before, or certainly not very much before.”

The president said he had discussed the option with Defence Secretary Jim Mattis, but did not indicate when he planned to implement it.

Mr Trump has promised a “big, beautiful wall” on the border since the early days of his campaign, claiming it will help secure the border. But Congress has yet to pass any meaningful funding for the wall’s construction, despite Mr Trump advocating for $25bn in the last major spending package.

The president has previously suggested funding the wall with money from the Pentagon budget, or making Mexico pay for it.

People strike across America for A Day Without Immigrants Show all 16 1 /16 People strike across America for A Day Without Immigrants People strike across America for A Day Without Immigrants Demonstrators march during the "Day Without Immigrants" protest in Chicago, Illinois, February 16, 2017. Theopolis Waters/Reuters People strike across America for A Day Without Immigrants Demonstrators march during the "Day Without Immigrants" protest in Washington, DC, U.S., February 16, 2017. Aaron P. Bernstein/Reuters People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. The crowd, which grew to well over a thousand participants, marched from the Austin City Hall to the Texas State Capital. Across the country hundreds of restaurants and eateries are closing for the day to protest President Trump's immigration policies and to highlight the contributions of immigrants to U.S. business and life. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants AUSTIN, TX - FEBRUARY 16: Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Demonstrators march during the "Day Without Immigrants" protest in Chicago, Illinois, February 16, 2017. Theopolis Waters/Reuters People strike across America for A Day Without Immigrants Demonstrators march during the "Day Without Immigrants" protest in Chicago, Illinois, February 16, 2017. Aaron P. Bernstein/Reuters People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. The crowd, which grew to well over a thousand participants, marched from the Austin City Hall to the Texas State Capital. Across the country hundreds of restaurants and eateries are closing for the day to protest President Trump's immigration policies and to highlight the contributions of immigrants to U.S. business and life. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants Protesters march in the streets outside the Texas State Capital on 'A Day Without Immigrants' February 16, 2017 in Austin, Texas. The crowd, which grew to well over a thousand participants marched from the Austin City Hall to the Texas State Capital. Across the country hundreds of restaurants and eateries are closing for the day to protest President Trump's immigration policies and to highlight the contributions of immigrants to U.S. business and life. Drew Anthony Smith/Getty People strike across America for A Day Without Immigrants High school student Kathia Suarez holds up a sign as she protests with others outside the Grayson County courthouse in downtown Sherman, Texas, Thursday, Feb. 16, 2017. LM Otero/AP People strike across America for A Day Without Immigrants High school senior Vicky Sosa holds a sign outside the Grayson County courthouse in downtown Sherman, Texas, Thursday, Feb. 16, 2017. In an action called "A Day Without Immigrants," immigrants across the country are expected to stay home from school, work and close businesses to show how critical they are to the U.S. economy and way of life. LM Otero/AP

Some 6,000 National Guard troops were deployed to the border in 2006, under president George W Bush. The troops did not participate in any law enforcement activity, but helped with surveillance and administrative tasks.

Mr Trump’s comments came as a “caravan“ of more than 1,000 South American immigrants made its way through Mexico towards the US border.

The migrants – many of whom are fleeing violence in their home countries – are making the journey together to stay safe, and to publicise their cause. Many will attempt to cross into the US, while others plan to stay in Mexico.

Donald Trump speaks to reporters about his DACA deal tweets

Mr Trump has tweeted about the migrants multiple times in recent days, warning that the caravan “had better be stopped” before it gets to the border.

“Border Patrol Agents are not allowed to properly do their job at the Border because of ridiculous liberal (Democrat) laws like Catch & Release,” Mr Trump tweeted on Sunday. ”Getting more dangerous. ‘Caravans’ coming. Republicans must go to Nuclear Option to pass tough laws NOW.”

Mr Trump has threatened to pull out of the North Atlantic Free Trade Agreement (Nafta) – a major trade deal between the US, Mexico, and Canada – if the caravan is not stopped. He also criticised a deal that Democrats had hoped to secure on DACA – a programme shielding childhood immigrants from deportation.

White House officials said this week that the administration was preparing for another push on immigration legislation. The proposals were similar to those the White House released in October, such as cracking down on sanctuary cities and reducing options for getting green cards, according to CNN.