The FBI is investigating a shooting in which one Border Patrol agent was killed and another wounded in the southern Arizona desert Tuesday, the first time an agent has been fatally shot since December 2010.

The pair were among several agents patrolling on horseback when the shooting occurred near Naco, about 100 miles southeast of Tucson and 50 miles from where Border Patrol agent Brian Terry was killed two years ago.

Terry’s killing was linked to the flawed “Fast and Furious” gun-tracking operation, run by the Bureau of Alcohol, Tobacco, Firearms and Explosives, after two guns tied to a suspect in the operation were found at the scene of Terry’s death.

Law enforcement officials said that no guns have been recovered and that no arrests have been made in the Tuesday shooting. The incident occurred about 1:50 a.m., after the agents responded to the activation of a ground sensor in the desert, according to George McCubbin, president of the National Border Patrol Council, a union that represents about 17,000 border agents. The sensors are used to alert agents to smugglers and illegal immigrants.

Officials identified the slain agent as Nicholas J. Ivie, 30. He and the other agents involved in the incident had been assigned to a Border Patrol station renamed in Terry’s memory. Ivie lived in Sierra Vista with his wife and their two young daughters.

“I am deeply saddened by the death of Border Patrol Agent Nicholas J. Ivie and the attack on another Border Patrol Agent early this morning,” said Homeland Security Secretary Janet Napolitano in a statement. “Both agents were on patrol near Bisbee, Arizona, when they came under fire from an unknown assailant. This act of violence reminds us of the risks our men and women confront, and the dangers they willingly undertake, while protecting our nation’s borders. We are working closely with our federal, state, and local law enforcement partners to track down those responsible for this inexcusable crime, and to bring them to justice.”

An FBI spokeswoman in Phoenix declined to comment except to say that the FBI is conducting its investigation along with the Cochise County Sheriff’s Office.

Law enforcement officials, speaking on the condition of anonymity because of the ongoing investigation, said federal agents were flooding the remote area in search of suspects and evidence.

“There’s no way to know at this point how the agent was killed, but because of Operation Fast and Furious, we’ll wonder for years if the guns used in any killing along the border were part of an ill-advised gun-walking strategy sanctioned by the federal government,” said Sen. Charles E. Grassley (R-Iowa), who started the investigation into the botched gun-trafficking investigation.

“We all mourn for the Border Patrol agent who was killed near the border station named after another fallen hero and fellow agent, Brian Terry,” Grassley said.

Thirteen Border Patrol agents have been killed in the line of duty in the past five years. Many of the deaths have been the result of injuries suffered in vehicle accidents.

“Today, for the second time in less than two years, a Border Patrol agent was murdered in the line of duty as he patrolled the southern Arizona desert,” said Rep. Ron Barber (D-Ariz.), who represents the area where the shooting occurred.

“This is a powerful reminder that our borders are far from secure and that every day the courageous men and women of the Border Patrol put their lives on the line while protecting the citizens of Arizona and the United States,” Barber said.

Barber recovered from a shooting last year in Arizona. The former district director for congresswoman Gabrielle Giffords was one of the 19 victims in the Tucson shooting that killed six and injured Giffords. Barber was elected in June to replace Giffords after she resigned from Congress.