The incident began when the unidentified man failed to stop Monday evening at the security gate at the Nevada National Security Site, located 70 miles (112 kilometers) north of Las Vegas, according to Darwin Morgan, spokesman for the National Nuclear Security Administration.

Morgan said the trespasser drove 8 miles (13 kilometers) with officers in pursuit before he parked and approached them with the object in his hand. Deputies and site officers fired at him when he ignored their verbal commands, Morgan said.

The man died at the property formerly known as the Nevada Test Site.

The FBI has been notified and no additional information has been released, Nye County sheriff’s Lt. David Boruchowitz said.

Nevada is currently involved in a legal battle with the U.S. Energy Department to block the shipment of a metric ton of weapons-grade plutonium to the site from South Carolina.

Government scientists conduct tests simulating nuclear explosions at the 1,360-square mile (3,522-square kilometer) site in Nevada that is larger than the state of Rhode Island.