Another 3,750 troops will be sent to the southern border to help install wire barriers and to monitor crossings, officials said. The new deployment will bring the total number of active-duty troops there to around 6,000.

In a tweet on Sunday, President Trump said that "STRONG border security" is necessary in the face of "Caravans marching through Mexico and toward our Country."

The announcement of new troops on Sunday comes just days before Trump is expected to discuss border security measures during Tuesday's State of the Union Address.

Acting Defense Secretary Patrick Shanahan said Thursdaythat the troops would be deployed to the border over the next month, NPR's Tom Bowman reported. They'll join the 2,300 active-duty troops already there, bringing the total to about the same number as were deployed in the fall. Another 2,100 National Guard troops are also stationed there.

"At the Pentagon, people I talk with say, listen: this is a waste of money," Bowman said. Stringing razor wire is a job better suited to the National Guard, they tell Bowman; "you don't use active-duty troops for this." Military troops deployed at the border "are not allowed to apprehend migrants the way border agents do," NBC Newsreported.

Last week around 2,400 migrants left a city shelter in Mexico City, on their way to the U.S.-Mexican border, Reuters reported.

When Pentagon officials testified before the House Armed Services Committee last week, they didn't mention the upcoming troop deployment. Congressman Adam Smith, who chairs the committee, released a statement criticizing what he called a lack of transparency.

"I am deeply troubled that the witnesses did not disclose the upcoming increase in guard, reserve, and active duty personnel, even though we asked them multiple times during a two-and-a-half-hour hearing what would happen next on the border," Smith wrote, echoing concerns in a letterhe wrote to Shanahan. That omission raises questions about whether the troop increase "is so unjustified that they cannot defend an increase in public," he wrote.

Trump suggested Friday that he would announce action on a border wall during the State of the Union address, which is taking place Tuesday. "I don't want to say it, but you'll hear the State of the Union, and then you'll see what happens right after the State of the Union," he told reporters.

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