The BBC, citing a report from the semi-official Iranian Students News Agency (ISNA) reported on Monday that the incident happened in an “explosive materials production unit” at the site that is south-east of the capital Tehran.

According to ISNA the blast was so powerful it shattered windows up to 12 kilometers away and the glare from the explosion lit up the night sky.

Several arms facilities and military bases are located east of the Iranian capital, including Parchin which UN nuclear inspectors have been seeking to visit to answer concerns about Iran’s atomic programme.