NOGALES, Ariz. » A U.S. Border Patrol agent opened fire on a group of people throwing rocks from across the Mexican border, possibly shooting one person, the agency said today.

The agents in Nogales, Ariz., had responded to reports of two suspected drugs smugglers near the border at about 11:30 p.m. Wednesday. The agents watched the two abandon a load of narcotics, then run back to Mexico, according to the Border Patrol.

As the agents approached to investigate, people on the Mexican side of the border began throwing rocks at them and ignored orders to stop, the agency said.

One agent opened fire, apparently striking a suspect, but injuries had not yet been confirmed today.

The Border Patrol said it has notified the Mexican government, and the FBI has begun an investigation.

The agency declined to comment further.

Border agents are generally allowed to use lethal force against rock throwers.

In 2010, a 15-year-old boy was shot and killed by a Border Patrol agent firing his weapon from El Paso, Texas, into Juarez, Mexico. Some witnesses said people on the Mexican side of the river, including the teen, were throwing rocks at the agent as he tried to arrest an illegal immigrant crossing the Rio Grande.

A federal judge in El Paso last year dismissed a lawsuit by the family of the boy because the teen was on the Mexican side of the Rio Grande when he was shot. U.S. law gives the government immunity when such claims arise in a foreign country, the judge noted.

A U.S. Department of Justice investigation, which included interviews with more than 25 civilian and law-enforcement witnesses, determined no federal civil rights charges could be pursued because “accident, mistake, misperception, negligence and bad judgment were not sufficient to establish a federal criminal civil rights violation.”

An investigation was ongoing over another fatal shooting by an agent last month after the Mexican government said a Mexican citizen was killed when the agent patrolling the Rio Grande fired his weapon across the border.

The Border Patrol said agents were aboard a boat near Laredo when a group of people began throwing rocks at them. One of the agents fired shots across the border toward Nuevo Laredo. The agency said it wasn’t clear whether anyone had been hit by bullets, but Mexico’s Foreign Relations Department issued a statement saying a Mexican citizen had been fatally shot.

The Mexican government at the time protested the use of what it called disproportionate force in immigration control and demanded a thorough investigation.