U.S Customs and Border Protection (CBP) over the weekend shut down traffic flowing into the country at a key point of entry on the southern border.

The move comes as agents work to secure the U.S.-Mexico border in anticipation of the so-called caravan, which reportedly includes thousands of Central American migrants seeking asylum in the United States.

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Lanes of traffic into the U.S. from Mexico at the San Ysidro Port of Entry have been shut down as agents lay down barbed wire, concrete and rebar to reinforce the entry point, NBC San Diego reported.

The San Ysidro port is the busiest land border crossing in the U.S., according to the outlet.

Pentagon officials earlier this month deployed thousands of active-duty military personnel to the border at Trump's request. Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE has emphasized that the troops are there as "border support" to help law enforcement as the migrants makes their way towards the country.

Trump on Saturday defended the decision to deploy around 5,800 troops to the border, saying, "They build great fencing, they built a very powerful fence."

“The fence is fully manned, nobody gets through," Trump added.

Critics accused the president of engaging in a political stunt by deploying the troops ahead of the midterm elections. Democrats and immigration activists claim Trump was seeking to stoke anti-immigrant and xenophobic fears in order to galvanize his base right before Election Day.

According to some estimates, the troop deployment could cost a total of $200 million, according to NBC San Diego.

More than 100 House Democrats earlier this month signed a letter to Mattis asking him to answer a number of questions on the mission, including its cost and duration.