WASHINGTON — Defense Secretary Jim Mattis extended the deployment of active-duty troops on the southwestern border into January, Defense Department officials said Tuesday.

The military’s border mission was slated to end Dec. 15, but the White House and the Department of Homeland Security had requested to continue using the troops as an additional bulwark against migrants from Central America entering the United States.

The requests came after Border Patrol agents fired tear gas at migrants trying to illegally enter the United States from Tijuana, Mexico.

The extended deployment would include aviation, medical, engineering and military police support, a Defense Department official said on Tuesday. That includes military planes to transport Border Patrol staff and setting up additional concertina wire.