MISSION, Texas (AP) — Authorities are concerned about the presence of private armed militias patrolling the border in search of people sneaking into the U.S. from Mexico.

The U.S. Border Patrol circulated an "issue paper" warning agents after a recent incident in Mission, Texas, in which armed men in fatigues showed up while agents were rounding up immigrants hiding in and around a canal near the Rio Grande.

The agents assumed the men who assisted them were part of a Texas Department of Public Safety tactical unit. But they later learned the men belonged to the Texas Militia, whose members dress like a SWAT team and carry weapons but have no law-enforcement training or authority of any kind.

The incident ended peacefully, but officials say it's easy to imagine a deadlier outcome.