Iranian media reported an explosion which was heard on Saturday night near Natanz was caused by an air defense drill, after local residents reported hearing a blast and seeing a bright light in the sky.

Initial reports indicated that Iranian air defense systems had been activated. According to the Iranian Fars News Agency, a bright light was seen in the sky as the explosion was heard.

A spokesman for the Iranian military later told Fars that the explosion was caused by an air defense missile that had been fired as part of a drill to test a quick response a possible attack. The spokesman stressed that there is "no need to worry."

The governor of Natanz County told Fars that no damage or casualties were reported in the incident.

The explosion comes as talks between Iran and world powers continue in Vienna in an attempt to return to the JCPOA nuclear deal.

The nuclear facility in Natanz has been targeted by attacks at least twice in the past two years.

In April, an explosion which Iranian officials blamed on Israel caused extensive damage at the site.

Fereydoon Abbasi-Davani, former head of Iran's Atomic Energy Organization, stated at the time that the nuclear site has been hit by five explosions in recent years.