PHOENIX (AP) — The FBI says a preliminary investigation has found friendly fire is likely to blame in the shootings of two border agents along the Arizona-Mexico border.

The shootings occurred Tuesday in a rugged area about five miles north of the border near Bisbee, Ariz.

Agent Nicholas Ivie and two others responded to an alarm triggered by a sensor aimed at detecting smugglers and others entering the U.S. illegally. Ivie was fatally shot. The wounded agent was struck in the ankle and buttocks and released from the hospital after surgery. The third agent wasn't injured.

Ivie's death marked the first fatal shooting of an agent since a deadly firefight with Mexican bandits that killed U.S. Border Patrol Agent Brian Terry in 2010 and spawned congressional probes of a botched government gun-smuggling investigation.

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

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Statement from FBI Phoenix Special Agent in Charge James Turgal:

While it is important to emphasize that the FBI’s investigation is actively continuing, there are strong preliminary indications that the death of United States Border Patrol Agent Nicholas J. Ivie and the injury to a second agent was the result of an accidental shooting incident involving only the agents.  The FBI is utilizing all necessary investigative, forensic, and analytical resources in the course of this investigation. We thank the United States Customs and Border Protection, United States Border Patrol, and the Cochise County Sheriff’s Office, for the challenging work they do every day and for their ongoing cooperation in this difficult matter.   At the appropriate time further information will be provided, but while the investigation continues it would be inappropriate to comment any further at this time.