President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Thursday threatened to close off the southern border, telling reporters that he would "close entry into the country" if immigration gets "uncontrollable."

"If we find that it gets to a level where we’re going to lose control or people are going to start getting hurt, we will close entry into the country for a period of time until we can get it under control," he said.

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Trump added that he meant the "whole border," though he appeared to be referring only to the southern border.

“We’re either going to have a border or we’re not," he said, adding that Mexico wouldn't "be able to sell their cars" into the U.S.

Trump also claimed that the U.S. closed the border earlier this week, though it was unclear what he was referring to.

Earlier this week traffic lanes near a key port of entry in San Diego were temporarily shut down.

“Two days ago, we closed the border. We actually just closed it," Trump said. "We said, ‘Nobody’s coming in.’ Because it’s out of control.”

Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenMore than million in DHS contracts awarded to firm of acting secretary's wife: report DHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections MORE said Monday that the lanes were shut down because a large number of migrants were planning to "rush the border."

Earlier this month, the Pentagon deployed roughly 5,800 troops to the border at the request of Trump.

The president has claimed that a group of Central American asylum seekers traveling through Mexico and toward the U.S. border present a national security threat.

"You're dealing with a minimum of 500 serious criminals, so I'm not going to let the military be taken of advantage of," Trump said Thursday. "I have no choice. Do I want that to happen? Absolutely not. You're dealing with rough people."

Homeland Security Department officials had said in a conference call with reporters earlier this week that they had identified 500 criminals traveling in the caravan, The New York Times reported.

Trump also confirmed Thursday that he had authorized troops at the border to use force against immigrants if necessary.