U.S. Army support of Operation Secure Line

U.S. Army troops weld steel pickets to install razor wire atop the U.S.-Mexico fence west of the DeConcini Port of Entry in Nogales.

WASHINGTON — The U.S. will be sending "several thousand" more American troops to the southern border to provide additional support to Homeland Security, Acting Defense Secretary Pat Shanahan says.

The troops will mainly be used to install additional wire barriers and provide increased surveillance of the area, he says. Plans call for about 150 more miles of concertina wire.

The Pentagon has approved an extended U.S. deployment to the border through the end of September. Officials have been working out how many forces are needed and which ones should be tapped.

Members of Congress pressed Pentagon leaders during a Capitol Hill hearing to better explain the deployment and what missions are suffering because troops are at the border.

There are about 2,400 U.S. forces working on the border mission.