A soldier agent sets up barbed wire at the San Ysidro port of entry, at the U.S.-Mexico border, seen from Tijuana, Mexico, Nov. 22, 2018. Credit: Ramon Espinosa | AP

The Pentagon will extend its mission along the southern border for eight months, the department said Monday, marking a significant lengthening of President Donald Trump’s involvement of the military in his effort to curb migration from Latin America.

Acting defense secretary Patrick Shanahan approved a request to provide the Department of Homeland Security with assistance though Sept. 30, 2019, the Pentagon said in a statement. Previously, the deployment of active duty forces along the border, which Trump ordered before the November midterm elections, was due to end Jan. 31.

The Pentagon “is transitioning its support at the southwestern border from hardening ports of entry to mobile surveillance and detection, as well as concertina wire emplacement between ports of entry,” the statement said. U.S. troops will also provide aviation support, the statement added.

It was not immediately clear how many additional troops the extended mission might require. Spokesmen for the Pentagon did not immediately respond to requests for details about the extended assignment.

The Pentagon has about 2,300 active-duty troops assisting the Department of Homeland Security on the southern border, down from a height of 5,900, a U.S. military spokesman, Mike Kucharek, said last week. About 1,100 soldiers and Marines are assigned to border support in California, with an additional 600 troops in Texas and 650 in Arizona.

The troops have helped place obstacles along the border and have supported Border Patrol personnel. There are also National Guard troops taking part in activities along the border.

In one major sign of the mission winding down, the military last month withdrew all troops from South Texas, including at a base camp in the border town of Donna, where hundreds of soldiers were based temporarily in November.

The military closed the camp shortly before Christmas, about five weeks after Homeland Security Secretary Kirstjen Nielsen and then-Defense Secretary Jim Mattis visited soldiers there.

The extension comes as Trump considers declaring a national emergency that could allow him to use military construction funds to build his border wall. Monday’s announcement did not immediately appear to be linked to that possibility, which would potentially produce an end to a standoff between the president and Democratic lawmakers that has resulted in an extended government shutdown.