Border Patrol agents came under fire Sunday evening near Nogales but were not injured.

The incident occurred at about 6 p.m. Sunday when agents were walking in the Bellota Canyon, located west of Nogales about five miles north of the U.S.-Mexico border, said Santa Cruz County Sheriff Tony Estrada. Three to four armed men started shooting at them.

The agents were not hit, and returned fire, Estrada said. None of the agents was hurt. And authorities don’t believe any of the armed men were hit either.

The Border Patrol sent a helicopter and its special response team to the area while Santa Cruz County Sheriff’s deputies combed the area looking for the possible shooters.

Nobody was apprehended, however. The FBI is handling the investigation.