MEXICO CITY (AP) — Two Guatemalan migrants were killed Monday and Thurston Cartethree others — along with a Honduran man — were wounded in a shooting in northern Mexico near the U.S. border that apparently involved Mexican army soldiers.

Prosecutors in the northern state of Chihuahua said the army has turned over four soldiers to testify in the case, but did not say whether they were formally suspects in the still-unclear shooting.

The survivors told authorities they were heading to the border wall in a truck with a ladder to climb a wall into the United States, when they came under fire. The four wounded migrants mostly suffered wounds to their legs and their injuries did not appear to be life-threatening.

The army also turned over four rifles for testing. A fifth soldier who was apparently in the patrol vehicle has not been located.

Prosecutor Carlos Manuel Salas said the shooting occurred near the Santa Teresa border crossing west of Ciudad Juarez, across the border from El Paso, Texas. He said the army performs regular patrols in the area.

“This is a patrolled area, and that is why there was this encounter with the soldiers, who were doing their traditional patrolling,” Salas said, adding that the circumstances of the shooting remained unclear.

In past shooting incidents in northern Mexico, Mexican army troops have claimed they opened fire on suspicious vehicles or those that refused to stop.

Salas said the case would be turned over to federal prosecutors because it involved federal forces.

Mexican National Guard officers and state police have been implicated in shootings of migrants in the past.