The Pentagon is expanding the military presence at the US-Mexico border.

It's planning to send 3,750 more troops to the broder, to put up more concertina wire and assist the Customs and Border Protection.

WASHINGTON (AP) — The Pentagon says it will send 3,750 more troops to the US-Mexico border to put up another 150 miles of concertina wire and provide other support for Customs and Border Protection.

The additions announced Sunday will bring the total number of active-duty troops on the border to 4,350.

The announcement is in line with what Acting Defense Secretary Pat Shanahan had said on Tuesday when he provided estimates for the next phase of a military mission that critics have derided as a political ploy by the White House.

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Shanahan said several thousand more troops would be sent mainly to install additional wire barriers and provide a large new system of mobile surveillance and monitoring of the border area. Sunday's announcement said the mobile surveillance mission would last through Sept. 30.

The initial deployment, which began in October as "Operation Faithful Patriot" (since renamed "border support"), was expected to end on December 15, 2018. The mission had previously been extended until the end of January.

Thousands of active-duty troops, nearly six thousand at the operation's peak, were sent to positions in California, Texas, and Arizona to harden points of entry, laying miles and miles of concertina wire. The number of troops at the southern border, where thousands of Central American migrants wait in hopes of entering the US, has dropped significantly since the operation began.