Lt. Johnny Hernandez of the Texas Department of Public Safety says the trooper was struck in the leg by what may have been an errant bullet from across the river.
Hernandez says it was unclear if the gunfight involved the Mexican military or state police. The Texas state trooper was hit about 1 p.m. Friday while on foot patrol in the Starr County border community of Fronton, about 105 miles upstream from Brownsville.
The trooper, whose identity hasn't been released, was airlifted to a McAllen hospital, where he was in stable condition with what Hernandez says is a non-life-threatening wound.