WASHINGTON – Thousands of active-duty troops deployed by President Donald Trump to the southwest border will be returning to their homes before the holidays, according to a Defense Department official.

Most of those coming home will be troops deployed to the Texas-Mexico border, said the official who was not authorized to speak publicly about the matter because it has not yet been announced. The precise number of those returning is unclear, the official said.

Trump ordered the deployment of active-duty troops to the border before the election in November to prepare for caravans of migrants from Central America who were streaming north toward the United States. The deployment was set to end Dec. 15, but it was extended for some last week by Defense Secretary Jim Mattis.

There are about 5,200 active-duty troops assigned to duty on the border, including 2,200 in Texas, 1,650 in California and 1,350 in Arizona, said Army Lt. Col. Jamie Davis, a Pentagon spokesman. The deployment of some units is scheduled to end on Dec. 15, Davis said, but he did not have a precise number for those leaving.

Mattis last week signed orders extending deployments for some troops through January. However, he told reporters Dec. 5 that troop levels would depend on requests from the Department of Homeland Security that the military is best able to perform, such as fortifying entry points.

Much of that work has been completed in Texas, Mattis said, adding that some combat engineers will remain behind.

"But a number of these troops will be coming off," Mattis said. "In other words, the continuation, first of all, is not of everybody. The missions that are done, they're coming home. So that will leave a modicum of engineers out there. You don't need many to move the last Jersey barriers or barbed wire barricades into position."

The Pentagon has provided Homeland Security with helicopter transportation units and military police.

There are an additional 2,100 National Guard troops on the border, and they are expected to remain there, Mattis said.