BISBEE, Ariz. » A Border Patrol agent was shot to death today in Arizona near the U.S.-Mexico line, the first fatal shooting of an agent since a deadly 2010 firefight with Mexican bandits that spawned congressional probes of a botched government gun-smuggling investigation.

The agent and a colleague were on patrol in the desert near Naco, Ariz., about 100 miles from Tucson, when shooting broke out shortly before 2 a.m., the Border Patrol said. The second agent was shot in the ankle and buttocks, and was airlifted to a hospital.

Authorities have not identified the agents, nor did they say whether any weapons were seized at the site of the shooting.

The last Border Patrol agent fatally shot on duty was Brian Terry, who died in a shootout with bandits near the border in December 2010. The Border Patrol station in Naco, where the two agents shot today were stationed, was recently named after Terry.

Terry’s shooting was later linked to the government’s Fast and Furious gun-smuggling operation, which allowed people suspected of illegally buying guns for others to walk away from gun shops with weapons, rather than be arrested.

Authorities intended to track the guns into Mexico. Two rifles found at the scene of Terry’s shooting were bought by a member of the gun-smuggling ring being investigated.

Critics of the operation say any shooting along the border now will raise the specter those illegal weapons are still being used in border violence.

"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," Republican Sen. Chuck Grassley said in a written statement.

The FBI, which also is investigating the shooting, declined to say whether investigators have recovered guns or bullet casings at the scene of the shooting.

The U.S. government has put thousands of sensors along the border that, when tripped, alert dispatchers that they should send agents to a given area.

The shooting occurred after an alarm was triggered on one of the many sensors along the border and the three agents went to investigate, said Cochise County Sheriff’s spokeswoman Carol Capas. It is not known whether the agents returned fire, Capas said.

The agents who were shot were on patrol with a third agent, who was not harmed, according to George McCubbin, president of the National Border Patrol Council, a union representing about 17,000 border patrol agents. The wounded agent was in surgery and expected to recover, McCubbin said.

Twenty-six Border Patrol agents have died in the line of duty since 2002.