Fire or explosion damages building at Iran nuclear site

A fire damaged a building on Thursday morning at one of Iran’s main nuclear facilities, a site that has previously been the target of cyberattacks and where enrichment activity has been ramped up in the past year.

Iranian officials downplayed the incident – the third prominent industrial accident in the country in recent days – though the BBC’s Farsi service said it received an email before the news of the fire was made public from a purported dissident group taking credit for what it said was an attack.

US satellite data showed an explosion or fire large enough to be detected from space breaking out at a building above the underground Natanz nuclear enrichment facility in central Isfahan province just after 2am.

The Atomic Energy Organisation of Iran (AEOI) said damage was sustained to an “industrial shed” that was under construction, with no casualties or release of radiation. The Natanz governor, Ramazanali Ferdowsi, was quoted by the state-linked Tasnim news agency as blaming a fire.

Footage later played on state media showed a brick building lined with ventilators with parts of its roof apparently blown off and the surrounding ground littered with debris. An image released by the AEOI appeared to show scorch marks and a door blasted from its hinges.

“There are physical and financial damages and we are investigating to assess,” Behrouz Kamalvandi, a spokesman for the AEOI, told Iranian state television. “There has been no interruption in the work of the enrichment site. The site is continuing its work.”

Journalists from the BBC’s Farsi service said on Thursday afternoon that some of them had received a statement – hours before the incident was publicised – from a group calling itself “Cheetahs of the Homeland”, which claimed to have carried out an “operation” at the Natanz facility, targeting an overground building so that the destruction would be “undeniable”.

The statement claimed the group was made up of dissidents within Iran’s defence establishment, but its veracity could not be independently confirmed.

Iranian officials did not raise the possibility of a hostile act but the country’s state-run IRNA news agency published commentary about the risk of attacks from the US and Israel.

“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.”

The US thinktank the Institute for Science and International Security said satellite analysis suggested the damaged building was the site of a centrifuge production workshop that it first publicly identified in 2017.

“A centrifuge assembly building could catch fire, but what I find interesting is that it’s this one, very sensitive building that catches fire or explodes,” said Fabian Hinz, a research associate at the James Martin Centre for Nonproliferation Studies in California.

He said the destruction of a centrifuge production facility could slow the advancement of the technology at the site and would be a useful target for Iran’s enemies.

The Natanz site, which includes buildings buried around 7.5 metres (25ft) underground to protect them from attacks, including airstrikes, is among the sites monitored by the International Atomic Energy Agency (IAEA) since Iran’s 2015 nuclear deal with the US and other countries.

Related: Iran nuclear experts race to stop spread of Stuxnet computer worm

From around 2007, the facility was targeted by a sophisticated and malicious computer virus known as Stuxnet that was widely thought to have been developed by the US and Israel – along with several western allies – and which played havoc with enrichment processes at the site by causing them to malfunction.

Since the US unilaterally pulled out of the nuclear deal in May 2018, the IAEA says Iran has been using Natanz to enrich uranium to about 4.5% purity, above the terms of the nuclear deal but below the weapons-grade threshold. It also has conducted tests on advanced centrifuges, according to the UN atomic agency.

Thursday’s fire followed an explosion last Friday that rattled Iran’s capital and came from an area in the eastern mountains that analysts believe hides an underground tunnel system and missile production sites. Iran has blamed the blast on a gas leak in what it describes a “public area”.

Associated Press contributed to this report