In a sharp escalation of border security efforts, U.S. and Mexican forces will soon begin synchronized patrols along their respective sides of the southern border, the Pentagon announced Wednesday.

Defense Secretary Pete Hegseth and Thomas D. Homan, President Trump’s border czar, toured areas near Mexico. By Reyes Mata III and Eric Schmitt Reyes Mata III reported from the southwestern U.S.

The plan would put a strip along the southern border under Pentagon control, allowing the military to detain migrants for trespassing on a military base until Border Patrol agents could arrest them.

Lt. Col. Phillip Mason stood on a narrow peninsula in early April just west of downtown San Diego, overlooking the coastal border between the U.S. and Mexico as a seasonal fog obscured the view. Mason ...