FRONTON, Texas — The U.S. Border Patrol says agents patrolling the Rio Grande have been shot at by gunmen from the Mexican side.

No agents were injured. But the agency says one of its boats was damaged by automatic weapons gunfire in the shooting around 2:30 a.m. Friday near the South Texas city of Fronton.

Agents on board estimated at least 50 rounds were fired by four gunmen. A Border Patrol spokesman couldn't immediately say whether the agents returned fire.

The Rio Grande separates the U.S. and Mexico in Texas. Border agents and Texas authorities routinely patrol the river and sometimes rescue migrants trying to cross.

The region across the river from Texas is dominated by violent gangs. U.S. authorities have forced thousands of asylum seekers to wait in Mexico, citing capacity issues.