A fire and an explosion struck a building above Iran’s underground Natanz nuclear enrichment facility early on Thursday.
It was a site that US-based analysts identified as a new centrifuge production plant.
The Atomic Energy Organisation of Iran sought to downplay the fire, calling it an “incident” that only affected an under-construction “industrial shed”, spokesman Behrouz Kamalvandi said.
However, both Kamalvandi and Iranian nuclear chief Ali Akbar Salehi rushed after the fire to Natanz, which has been targeted in sabotage campaigns in the past.
Mr Kamalvandi did not identify what damaged the building, though Natanz governor Ramazanali Ferdowsi said a “fire” had struck the site, according to a report by the semi-official Tasnim news agency.
Authorities offered no cause for the blaze, though Iran’s state-run IRNA news agency published a commentary addressing the possibility of sabotage by enemy nations such as Israel and the US following other recent explosions in the country.
“The Islamic Republic of Iran has so far tried to prevent intensifying crises and the formation of unpredictable conditions and situations,” the commentary said.
But “the crossing of red lines of the Islamic Republic of Iran by hostile countries, especially the Zionist regime and the US, means that strategy … should be revised.”
A photograph later released by the atomic energy agency and state TV video showed a brick building with scorch marks and its roof apparently destroyed. Debris on the ground and a door that looked blown off its hinges suggested an explosion accompanied the blaze.
Data collected by a US National Oceanic and Atmospheric Administration satellite suggested the fire broke out around 2am local time in the north-west corner of the Natanz compound. Flames from the blaze were bright enough to be detected by the satellite from space.
“There are physical and financial damages and we are investigating to assess,” Mr Kamalvandi told Iranian state television. “Furthermore, there has been no interruption in the work of the enrichment site. Thank God, the site is continuing its work as before.”
The site of the fire corresponds to a newly opened centrifuge production facility, said Fabian Hinz, a researcher at the James Martin Centre for Nonproliferation Studies at the Middlebury Institute of International Studies in Monterey, California.