US President Donald Trump has said he would use US military forces to protect the nation's southern border with Mexico until there is a border wall and "proper security" in place.
"We are going to be doing things militarily," Mr Trump told reporters at the White House, adding he had discussed the idea with US Defense Secretary Jim Mattis.
"Until we can have a wall and proper security were going to be guarding our border with the military. That’s a big step," he said.
"We cannot have people flowing into our country illegally, disappearing, and by the way, never showing up for court."
Earlier, Mr Trump had said US foreign aid to Honduras and other countries was at risk unless they stopped what he called a "caravan" of more than 1,200 Central American migrants headed to the US border with Mexico on a 3,200km journey from the Mexico-Guatemalan border.
Mexico's government has said such "caravans" of mostly Central Americans, including many escaping violence in Honduras, have occurred since 2010.
Mr Trump has stepped up his immigration rhetoric in recent days and his administration has moved to further crack down on people who are in the United States illegally.
Mr Trump has already blasted Mexico and threatened to upend the North American Free Trade Agreement (NAFTA) over the caravan.
The current trip has also put pressure on Mexican authorities ahead of the 1 July presidential election there.
"We will be doing things with Mexico, and they have to do it, otherwise I’m not going to do with the NAFTA deal," Mr Trump said.
US presidents have ordered National Guard forces to the border in the past.
Under President George W Bush, National Guard forces from all US states and territories were used between 2006 and 2008 for things such as border-related intelligence analysis, but did not have a direct law enforcement role, according to the Pentagon.
Yesterday, Mr Trump railed against Democrats over immigration and again pressed US policymakers to pass legislation to build his long-promised border wall.
Despite months of efforts, no immigration deal has emerged in the Republican-led Congress, where much major legislation is not expected to pass ahead of November's midterm congressional elections.
