A massive explosion at Iran’s Parchin nuclear plant killed two people, Iran’s state news agency IRNA reported. The report said a fire broke out at the plant on Sunday night and gave no further details.

The BBC, citing the semi-official Iranian Student News Agency (ISNA), said that the incident occurred at an “explosives materials production unit” south-east of the Iranian capital of Tehran.

According to ISNA, the blast was so powerful that it shattered windows located 15 kilometers away. Witnesses reported seeing a glare from the explosion that lit up the night sky.

While Iranian officials are not commenting on the incident, they did confirm that there was an “incident” at the Parchin plant. Two people have been classified as “missing.”

Several military bases and weapon facilities are located east of Tehran in close proximity to the Parchin site. UN nuclear inspectors have been attempting to gain access to the site from Iranian officials as part of an investigation into Iran’s nuclear program.

Investigators believe that the Parchin site is being used to research and test sophisticated explosives that could potentially be used to detonate a nuclear warhead. The Islamic Republic has reiterated that IAEA inspectors would not be granted access to the site.

Last month, Israel Internal Security Minister Yuval Steinitz said that Israel had “reliable information” that Parchin was being used to develop Iran’s nuclear weapon capabilities.

Inspectors have been denied access to Parchin since 2005. Iran maintains that the nuclear facility is being used for purely civilian purposes.

Nuclear experts from the IAEA are set to begin talks Tuesday in Tehran to resolve issues regarding Iran’s nuclear program. The deadline to reach a permanent agreement between the P5+1 and the Islamic Republic on their nuclear program is November 24.