Mexican federal police arrested two men who may be connected with the fatal shooting of a U.S. Border Patrol agent this week just north of the Mexico/Arizona border.

A Mexican law enforcement official, who spoke on condition of anonymity because he was not authorized to release the information, said it remained unclear if there was strong evidence linking the men to the shooting of Agent Nicholas Ivie. Another agent was wounded in the attack.

Ivie and two other agents were fired upon in a rugged hilly area about five miles north of the border as they responded to an alarm that was triggered on one of the sensors that the government has installed along the border.

No weapons have been found, according to a federal law enforcement official who spoke on the condition of anonymity because information on the search hasn't been publicly released.

Agents and deputies were searching the area on ATVs, horseback and on foot with up to four helicopters overhead in the southern foothills of the Mule Mountains that's considered a known smuggling area.

Ivie lived in Sierra Vista with his wife and their two young daughters.

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 Tuesday 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 raises the specter that 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 statement.

The Terry family said that the shooting was a "graphic reminder of the inherent dangers that threaten the safety of those who live and work near the border."

Authorities set up a checkpoint on a dirt road about seven miles southeast of Bisbee. Border Patrol agents at the checkpoint declined to comment and barred reporters from going further.

The agents were fired upon in a rugged hilly area about five miles north of the border as they responded to an alarm that was triggered on one of the sensors, said sheriff's spokeswoman Carol Capas. It wasn't immediately known whether the agents returned fire, she said.

The Border Patrol said Ivie worked for the agency since January 2008 and grew up in Provo, Utah. He worked as an emergency medical technician before joining the Border Patrol, said his brother-in-law, Todd Davis. He served a two-year mission with The Church of Jesus Christ of Latter-day Saints in Mexico City after high school.

Davis said Ivie's desire to help others, and his love of the outdoors and riding horses led him to the Border Patrol, where he served on the horse patrol unit.

"Nick always tried to help others. He was a very selfless man with his family, with his friends, in anything he did," Davis said. "You know the risk but you pray this day would never happen."

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

Based on reporting by the Associated Press.

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