WASHINGTON — Acting Defense Secretary Patrick Shanahan has told Congress that the military needs to return to its traditional missions, and he wants to know how much longer troops will be needed at the U.S.-Mexico border.

Shanahan tells a House appropriations subcommittee that he needs to determine how many more agents and other workers the Homeland Security Department must have to fulfill the border mission.

His comments come just days after the Pentagon said it would send 320 more active-duty troops to the border for tasks that put them in closer contact with migrants. Those duties include driving buses, serving food and providing medical support.

President Donald Trump ordered more than 5,000 active-duty forces to the border last October to help construct wire barriers and support the border patrol.