A U.S. Border Patrol agent shot and killed a man Sunday in the Baboquivari Mountains on the Tohono O'odham Nation, federal officials confirmed Tuesday.

The incident occurred about midday Sunday when an agent encountered a group of people who had crossed the border illegally, agency spokesman Victor Brabble said via email.

A struggle occurred during the incident, leading to the agent shooting one member of the group.

Brabble did not give the nationality of the man who died.

The FBI is investigating, Special Agent in Charge James Turgal said Tuesday.

Sunday's incident was the third fatal shooting by a Border Patrol agent in the Tucson Sector since Oct. 2. That day, agent Nicholas Ivie was killed in what the FBI has determined was a case of friendly fire.

On Oct. 10, an agent in Nogales, Ariz., fired across the border and killed 16-year-old José Antonio Elena Rodríguez. The FBI and Mexican authorities are also investigating the killing of Elena Rodríguez.

Contact reporter Tim Steller at 807-8427 or tsteller@azstarnet.com