Missing nuclear material or a gas leak could be behind the spate of drone sightings in recent weeks, an expert has suggested.

None of the mysterious drones reported over the skies of the US Northeast are being flown by the Pentagon or are part of secret government tests, a Defense Department spokesman said Tuesday.

The link between "drone" sightings and radioactive material stemmed from the U.S. Nuclear Regulatory Commission's alert about "lost" medical equipment this month.

Belleville Mayor Michael Melham has theorized that the lights people have been seeing above Essex County are ‘looking for something’

What might they be looking for? Maybe that's radioactive material," Belleville, NJ, Mayor Michael Melham said Tuesday.