A U.S. Border Patrol agent has been killed and another wounded in a shooting in the southwestern state of Arizona near the border with Mexico.

The agents were shot early Tuesday while patrolling on horseback in the town of Naco, Arizona.

The Department of Homeland Security says the wounded agent was airlifted to a hospital with non-life threatening injuries. Officials say a third agent was unharmed.

Authorities have not yet identified the agents involved or indicated who may have been behind the shooting. The Federal Bureau of Investigation and the local sheriff's office are investigating.

Both of the agents shot Tuesday were assigned to a patrol station recently renamed after the last U.S. Border Patrol agent to be fatally shot in the line of duty — Brian Terry. Terry was killed in a shootout with Mexican bandits near the border in December 2010.

That killing took place during a controversial operation known as “Fast and Furious,” in which U.S. federal agents allowed guns to be smuggled into Mexico, hoping they would lead them to arms traffickers. But agents lost track of most of the weapons, two of which were used in the murder of Agent Terry.