US President Donald Trump, further escalating his rhetoric on illegal immigration, has said that the military will be sent to guard the US-Mexico border until his long-promised border wall is built.

Speaking to reporters during a news conference with the Presidents of three Baltic nations — Estonia, Latvia and Lithuania — Trump on Tuesday described existing immigration laws as “lax and ineffective” and called for militarising the border with Mexico to prevent an influx of Central American migrants he said were ready to stream across it.

“We have horrible, horrible and very unsafe laws in the US,” Trump said. “We are preparing for the military to secure our border between Mexico and the US.”

He continued: “We cannot have people flowing into our country illegally, disappearing, and by the way never showing up for court.” Trump said he would soon meet Defence Secretary Jim Mattis to discuss having the US military deployed to the border, the US media reported.

But he offered no details about how the military would be used. Later Tuesday, White House Press Secretary Sarah Huckabee Sanders confirmed that the administration’s plans include mobilising the National Guard.

Trump was briefed on the possibility of sending troops to the border last week by Homeland Security Secretary Kirstjen Nielsen and White House aides and he loved the idea, said a senior White House official.

He added that senior policy adviser Stephen Miller was involved in the planning.

“Sending US service members to patrol the US-Mexico border is wrong,” tweeted Representative Beto O’Rourke, who represents the border city of El Paso and is running for the US Senate against Republican Senator Ted Cruz. “It’s dangerous to service members, to US citizens, and to the people of the border.”

But officials representing Border Patrol agents applauded Trump’s announcement. Brandon Judd, the president of the National Border Patrol Council, said deploying military personnel would be a “tremendous boon”, the Washington Post reported.

Members of the military cannot arrest immigrants because they are not duly sworn law enforcement personnel, Judd said, but they can aid Border Patrol agents by serving as their de facto “eyes” surveying the border.

Mexico expressed opposition to the idea, asking for a clarification on the announcement by @POTUS about the use of the Army on the border. “The Mexican government will define its reaction on the basis of that clarification and always in defence of our sovereignty and national interests,” Mexican Foreign Secretary Luis Videgaray tweeted.

The Obama administration sent 1,200 National Guard troops to the southern border in 2010 to assist Border Patrol and immigration officials amid rising concerns about drug trafficking.