President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE's strategy to combat illegal crossings and drug trafficking at the U.S. southern border would include mobilizing the National Guard, the White House said Tuesday.

The statement appeared to clarify an announcement by Trump earlier Tuesday, in which he proposed sending the military to guard the southern border until his long-promised border wall is built, without providing further details.

The statement did not provide details about when or if the strategy would actually be carried out.

Sending the National Guard to patrol the border would not be unprecedented.

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Former President George W. Bush sent 6,000 National Guard troops to the southern border in 2006 to assist the Border Patrol while more border agents were hired and trained. And former President Obama sent 1,200 guardsmen to the U.S.-Mexico border in 2010.

Trump has stepped up his rhetoric on illegal immigration in recent days, echoing the hard-line talk that often characterized his presidential campaign and early days in the White House.

On Sunday, he closed the door on a potential deal with lawmakers on the Obama-era Deferred Action for Childhood Arrivals program, and called on Monday for Mexico to step up efforts to detain immigrants who illegally pass through its borders.

Those comments apparently followed a briefing last week in which senior officials warned Trump of the "growing influx of illegal immigration, drugs and violent gang members from Central America, and directed a vigorous administrative strategy to confront this threat and protect America’s national security," according to the White House.

Trump's suggestion on Tuesday that he would militarize the southern border also came after reports that he had floated having the Pentagon redirect funding to pay for the wall, a move that would require congressional approval he would be unlikely to receive.

"Until we can have a wall and proper security, we are going to be guarding our border with the military," Trump said at the White House on Tuesday. "That's a big step. We really haven't done that before, or certainly not very much before."

That comment prompted the Mexican government to lodge a formal request that the State Department and Homeland Security Department clarify the president's remarks.