FILE - In this June 21, 2006, file photo, members of the California National Guard work next to the U.S.-Mexico border fence Wednesday, June 21, 2006, near the San Ysidro Port of Entry in San Diego. President Donald Trump said April 3, 2018, he wants to use the military to secure the U.S.-Mexico border until his promised border wall is built. The Department of Homeland Security and White House did not immediately respond to requests for comment. At the Pentagon, officials were struggling to answer questions about the plan, including rudimentary details on whether it would involve National Guard members, as similar programs in the past have done. But officials appeared to be considering a model similar to a 2006 operation in which former President George W. Bush deployed National Guard troops to the southern border in an effort to increase security and surveillance.(AP Photo/Denis Poroy, File)
FILE - In this June 21, 2006, file photo, members of the California National Guard work next to the U.S.-Mexico border fence Wednesday, June 21, 2006, near the San Ysidro Port of Entry in San Diego. President Donald Trump said April 3, 2018, he wants to use the military to secure the U.S.-Mexico border until his promised border wall is built. The Department of Homeland Security and White House did not immediately respond to requests for comment. At the Pentagon, officials were struggling to answer questions about the plan, including rudimentary details on whether it would involve National Guard members, as similar programs in the past have done. But officials appeared to be considering a model similar to a 2006 operation in which former President George W. Bush deployed National Guard troops to the southern border in an effort to increase security and surveillance.(AP Photo/Denis Poroy, File) Credit: DENIS POROY

Washington — President Donald Trump and border-state governors are working to “immediately” deploy the National Guard to the U.S.-Mexico border to fight illegal immigration, Homeland Security Secretary Kirstjen Nielsen said on Wednesday.

“The threat is real,” Nielsen said, 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 wanted to use the military to secure the southern border until his long-promised border wall is erected.

Nielsen said she’s been in touch with governors on the southwest border states and has been working with them to develop agreements that will oversee where and how many Guardsmen will be deployed. She suggested some troops could begin arriving as soon as Wednesday night, though other administration officials cautioned that details on troop levels, locations and timing still were being worked out.

“We do hope that the deployment begins immediately,” she said.

Trump has been frustrated by slow action on building his “big, beautiful wall” along the Mexican border — the signature promise of his campaign — as well as a recent uptick in illegal border crossings that had plunged during the early months of his presidency. He also has been fixated on the issue of border security since he grudgingly signed a spending bill last month that includes far less money for the wall than he’d hoped for.

Federal law prohibits the use of active-duty service members for law enforcement inside the U.S., unless specifically authorized 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.

Nielsen said the effort would be similar to a 2006 operation in which President George W. Bush deployed troops to help U.S. Customs and Border Protection personnel with non-law enforcement duties while additional border agents were hired and trained. President Barack Obama also sent about 1,200 troops in 2010 to beef up efforts against drug smuggling and illegal immigration.

Nielsen said her department had developed a list of locations where it would like assistance and was discussing with the governors how to facilitate the plans. She declined to say how many personnel would be needed or how much the operation would cost, but she insisted, “It will be as many as is needed to fill the gaps that we have today.”

One congressional aide said that lawmakers anticipate 300 to 1,200 troops will be deployed and that the cost of the deployment was expected to be at least $60 million to $120 million a year. The Pentagon likely can reprogram funds in the short term but probably would need authorization from Congress beyond a few months, said the aide, who wasn’t authorized to speak publicly and spoke on condition of anonymity.

The Republican governors of Texas and Arizona applauded the move, while New Mexico Gov. Susana Martinez, also a Republican, didn’t immediately comment on it. Democratic Gov. Jerry Brown of California, who has been sparring with Trump over immigration policies, is likely to oppose it.