It is done under the authority of the national emergency on the border declared by President Donald Trump on his first day in office.U.S. authorities say the zones are needed to close gaps in border enforcement and help in the wider fight against human smuggling networks and brutal drug cartels.

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.