Trump sends National Guard to US-Mexican border to stop illegal immigration

President Donald Trump and border-state governors are working to "immediately" deploy the National Guard to the US-Mexico border to fight illegal immigration, with some troops potentially arriving later yesterday, Homeland Security Secretary Kirstjen Nielsen said.

"The threat is real, "Nielsen said at an afternoon briefing, adding that Trump was signing a proclamation to put the deployment into effect. "It's time to act."

The announcement came hours after Trump pledged "strong action today" on immigration and a day after he said he wants to use the military to secure the southern border until his "big, beautiful wall" is erected.

In a tweet early yesterday, Trump said that "Our Border Laws are very weak" and that Democrats "stand in our way" of new laws. He added, "We will be taking strong action today."

Trump told reporters on Tuesday that he'd been discussing the idea of using the military at the border with Defence Secretary Jim Mattis.

"We're going to be doing things militarily. Until we can have a wall and proper security, we're going to be guarding our border with the military," Trump said, calling the move a "big step."

Federal law prohibits the use of active-duty service members for law enforcement inside the US, unless specifically authorised by Congress. But over the past 12 years, presidents have twice sent National Guard troops to the border to bolster security and assist with surveillance and other support. The White House counsel's office has been working on the idea for several weeks, according to a senior official who spoke on condition of anonymity to discuss internal plans.

Trump has been frustrated by slow action on building a wall along the Mexican border. He's previously suggested using the Pentagon's budget to pay for the wall, arguing it is a national security priority, despite strict rules that prohibit spending that's not authorised by Congress.

Nielsen said the administration was considering a model similar to a 2006 operation in which President George W. Bush deployed National Guard troops to the southern border, with a focus on assisting US Customs and Border Protection personnel.

"We are anxious to have the support," she said.

Under Operation Jump Start, 6,000 National Guard troops were sent to assist the border patrol with non-law enforcement duties while additional border agents were hired and trained.

Over two years, about 29,000 National Guard forces participated as forces rotated in and out. The Guard members were used for surveillance, communications, administrative support, intelligence, analysis and the installation of border security infrastructure.

In addition, President Barack Obama sent about 1,200 National Guard troops to the US-Mexico border in 2010 to beef up efforts against drug smuggling and illegal immigration.

Texas also deployed military forces to its 1,290 kilometre border with Mexico. Former Texas Governor Rick Perry, now Trump's energy secretary, sent 1,000 Texas National Guardsmen to the Rio Grande Valley in 2014 in response to a sharp increase in Central American children crossing the border alone.