The blast was heard in the area of Badroud, around 12 miles from the Natanz nuclear site, according to IRNA, Iran’s state news agency. The incident involved a sound and then a flash of light in the sky, reported Fars News Agency, an organization close to the Islamic Revolutionary Guard Corps.

Natanz has been the site of attacks and sabotage in the past, but Iran didn’t immediately place blame on any foreign government and sent differing signals about what happened after reports of the explosion circulated in local media.

An Iranian army spokesman played down the explosion on state television, saying a missile system had been test fired and there was no reason to be concerned. A news agency close to Iran’s security forces, Tasnim, cited sources saying that a hostile drone had activated defense systems on Saturday night.