A handout picture provided by the Iranian presidential office on Saturday shows a video conference screen of an engineer inside Iran's Natanz uranium enrichment plant - Iranian Presidency/AFP

A blast was reported Saturday in the vicinity of a nuclear site in Natanz, Iran, according to preliminary reports.

The explosion was heard in the skies over the Iranian city of Badroud, just 20 kilometers (12 miles) from the nuclear plant, the official IRNA news agency reported.

“Badroud residents heard the noise and saw a light which showed an object had just blown up in the skies over the city,” a witness told IRNA.
Several media outlets including Nour News, a website linked to Iran’s Revolutionary Guards, said the explosion was not an attack, but rather was caused by a missile as part of a test of air defenses’ response to a potential attack.

Some of the reports said a drone was shot down.

The explosion came amid heightened tensions between Iran and world powers, as Tehran continues to race forward with its nuclear enrichment. It came a day after nuclear negotiations were halted in Vienna, with Western countries saying Iran had come to the talks with unrealistic proposals.

Iran’s uranium enrichment facilities in Natanz have seen several reported attacks in recent years which have been attributed to Israel.

In April, the underground nuclear facility there experienced a mysterious explosion that damaged some of its centrifuges. Last July, unexplained fires struck the advanced centrifuge assembly plant at Natanz, which authorities later described as sabotage.