Shots rang out while the agents were patrolling near Fronton, Texas, the Rio Grande City Station Marine Unit reported. Agents saw four people with automatic weapons on the Mexican riverbank, CPB reported.
The incident is under investigation.
Three ports of entry — Rio Grande City, Roma and Falcon Dam — are located in the territory. Directly across the Rio Grande are the Mexican cities of Ciudad Camargo, Miguel Aleman, Mier and Nuevo Guerrero, all located in Tamaulipas, one of Mexico’s 31 states.