Annexed militarized zones will soon cover nearly one-third of the U.S. border with Mexico, empowering soldiers to arrest people who cross the border illegally.

The military is expanding its authority and reach along swaths of the southern U.S. border where troops have been empowered to detain people who enter the country illegally.

The Pentagon is establishing a fourth military defense zone along the U.S.-Mexico border, where American soldiers can apprehend noncitizens on charges of trespassing, Chief Pentagon spokesman Sean Parnell said Wednesday.