The U.S. Border Patrol says its agents discovered an active round of ammunition apparently from a circa World War II piece of artillery.
The agency's Tucson sector says the unexploded device was found Friday in Bisbee, Arizona near the international boundary fence with Mexico.
It says deputies from the Cochise County Sheriff's Office helped set up a safety perimeter around the device to keep people away from it.
An explosives expert from Davis-Monthan Air Force Base on Tuesday examined the ammunition, determined it was live and detonated it in place.
There was no word on where the ordnance might have come from.