PHOENIX — A U.S. Border Patrol agent opened fire on a group of people throwing rocks from across the Mexican border, killing a teenage boy and eliciting outrage from the Mexican government over the use of lethal force, authorities said Thursday.

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. A Mexican official with direct knowledge of the investigation said Thursday a 16-year-old boy was killed in the shooting. The person spoke on condition of anonymity because they were not yet authorized to discuss details of the case.

The Sonora state attorney general's office in Mexico said in a statement Thursday that Jose Antonio Elena Rodriguez, 16, from Nogales, Sonora, was found dead at the border from gunshot wounds about midnight Wednesday.

However, the office didn't definitively confirm the boy had been shot by the agent, only noting that police received reports of gunshots, then found his body on a sidewalk near the border barrier.

Mexico's Foreign Relations Department issued a statement later saying it "forcefully condemned" the shooting and calling such deaths "a serious bilateral problem."

"The disproportionate use of lethal force during immigration control actions is unacceptable under any circumstances. The repeated nature of this type of cases has drawn a reaction of rejection from Mexican society and all of the country's political forces."

The department said it had asked U.S. authorities for a "exhaustive, transparent and timely investigation" of the shooting.

The Border Patrol declined to comment further and would only say in a statement that one person "appeared to have been" shot by the agent. The FBI was investigating.

Ricardo Alday, a spokesman for the Mexican Embassy in Washington, said in a statement that Mexican authorities will also investigate.

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."

In 2011, a Border Patrol agent shot and killed a man climbing a fence along the Arizona-Mexico. Cochise County sheriff's investigators said at the time there was no indication the 19-year-old assaulted or tried to assault the agent when he was shot three times in the back while climbing a ladder trying to cross the border back into Mexico.

Investigators later found 48 pounds of marijuana in the back of the man's truck. An investigation into the shooting is ongoing.

Another investigation also remains active into a shooting last month by an agent patrolling the Rio Grande.

The Border Patrol said agents were aboard a boat near Laredo, Texas, 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.

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Associated Press writer Mark Stevenson in Mexico City contributed to this report.

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  • In this photo taken Thursday, Aug. 9, 2012, A U.S. Border Patrol vehicle keeps watch along the border fence in Nogales, Ariz. A U.S. Border Patrol agent opened fire on a group of people throwing rocks from across the Mexican border, killing a teenage boy and eliciting outrage from the Mexican government over the use of lethal force, authorities said Thursday.(AP Photo/Ross D. Franklin)

  • In this photo taken Thursday, Aug. 9, 2012, vehicles drive along the border fence in Nogales, Mexico. A U.S. Border Patrol agent opened fire on a group of people throwing rocks from across the Mexican border, killing a teenage boy and eliciting outrage from the Mexican government over the use of lethal force, authorities said Thursday, Oct. 11, 2012. (AP Photo/Ross D. Franklin)

  • In this photo taken Thursday, Aug. 9, 2012, vehicles drive along the border fence in Nogales, Mexico. A U.S. Border Patrol agent opened fire on a group of people throwing rocks from across the Mexican border, killing a teenage boy and eliciting outrage from the Mexican government over the use of lethal force, authorities said Thursday, Oct. 11, 2012. (AP Photo/Ross D. Franklin)

  • Border patrol agents carry the casket of agent Nicholas Ivie during Ivie's funeral at the UCCU Center at Utah Valley University in Orem on Thursday, Oct. 11, 2012. Agent Ivie, a Provo, Utah native, was killed in a shooting at the Arizona-Mexico border October 2nd. (AP Photo/The Salt Lake Tribune, Francisco Kjolseth) DESERET NEWS OUT; LOCAL TV OUT; MAGS OUT

  • Nicholas Ivie

    In this undated photo provided by the Ivie family, Border Patrol Agent Nicholas Ivie is seen. Ivie, a 30-year-old father of two, was shot and killed in the sparsely populated desert in southeastern Arizona early Tuesday, Oct. 2, 2012. (AP Photo/Ivie Family, Cole Kynaston)

  • In this photo provided by U.S. Customs and Border Protection, law enforcement forces and equipment gather at a command post in the desert near Naco, Ariz., Tuesday, Oct. 2, 2012, after a Border Patrol agent was shot to death near the U.S.-Mexico line. The agent, Nicholas Ivie, 30, and a colleague were on patrol about 100 miles from Tucson, when shooting broke out shortly before 2 a.m., the Border Patrol said. (AP Photo/U.S. Customs and Border Protection, Gabriel Guerrero)

  • FILE - In this April 19, 2011, file photo, a member of the National Guard checks on his colleague inside a Border Patrol Skybox near the Hidalgo International Bridge in Hidalgo, Texas. Illegal immigration has slowed in recent years, with the Border Patrol recently recording the fewest arrests in almost 40 years. But many people worry that the Mexican border, the most popular crossing point for newly arriving undocumented immigrants, still isn

  • Det. Bill Silva, left, with the Bisbee Police Department, and an unnamed agent with the Drug Enforcement Administration patrol a fence line east of Naco, Ariz., after a Border Patrol agent was killed early Tuesday, Oct. 2, 2012. The shooting occurred after an alarm was triggered on one of the thousands of sensors placed by the U.S. government along the border, and the agents went to investigate, said Cochise County Sheriff's spokeswoman Carol Capas. (AP Photo/Arizona Daily Star, Mike Christy) NO MAGS NO SALES, MANDATORY CREDIT

  • A 72-foot long helium-filled balloon flies 2,500 feet above the U.S.-Mexico border, Wednesday, Aug. 22, 2012, near Roma, Texas. The Border Patrol is testing the surveillance balloons on loan from the Defense Department to see if they could be as effective spotting undocumented immigrants and drug smugglers as they were spotting insurgents in war zones. (AP Photo/Christopher Sherman)

  • This undated photo provided by the U.S. Border Patrol shows an aerostat like those being tested along the U.S.-Mexico border, Wednesday, Aug. 22, 2012, near Roma,Texas. The Defense Department has loaned the helium-filled surveillance balloons to Border Patrol to see if they could be as effective for border security as they were in war zones. (AP Photo/U.S. Border Patrol)

  • In this Thursday, Dec. 16, 2010 picture, U.S. Border Patrol vehicles drive from a checkpoint, as teams of border officers comb the Arizona desert about 10 miles north of Mexico in search for a suspect in the fatal shooting of U.S. Border Patrol agent Brian Terry in the rugged terrain in Rio Rico, Ariz. The shooting Tuesday night came after agents spotted suspected bandits known for targeting undocumented immigrants along a violent smuggling corridor, National Border Patrol Council President T.J. Bonner said. Terry, 40, was waiting with three other agents when the gunbattle erupted. Terry died in the shooting. None of the other agents were injured. (AP Photo/Ross D. Franklin)