Federal authorities have probed a rash of reported sightings of unmanned drones flying about a former nuclear weapons site in South Carolina, but say none could be verified.

The U.S. Energy Department says it investigated a dozen reported sightings since June at the sensitive Savannah River Site. The Augusta Chronicle reported the Energy Department briefed a local citizens board Monday about their findings.

The agency’s conclusion? No drones were found or confirmed.

Pilots have long been told to avoid airspace over the Savannah River Site near South Carolina’s line with Georgia. So, when the sightings were first reported, the site made public address announcements and sent emails to its workers to watch the skies. Security guards even checked vehicles, trying to ferret out drones or their pilots.

(AP)