Iran will retaliate against any country that carries out cyber attacks on its nuclear sites, the head of civilian defence said, after a fire at its Natanz plant which some Iranian officials said may have been caused by cyber sabotage.
The Natanz uranium-enrichment site, much of which is underground, is one of several Iranian facilities monitored by inspectors of the International Atomic Energy Agency (IAEA), the UN nuclear watchdog.
An online video and messages purportedly claiming responsibility for a fire that analysts say damaged a centrifuge assembly plant at the nuclear site deepened the mystery around the incident - even as Tehran insisted it knew the cause but would not make it public due to "security reasons."
The multiple, different claims by a self-described group called the "Cheetahs of the Homeland" included language used by several exiled Iranian opposition organisations. They also focused almost entirely on Iran's nuclear programme, viewed by Israel as a danger to its very existence.
The disparate messages, as well as the fact that Iran experts have never heard of the group before, raised questions about whether Natanz again had faced sabotage by a foreign nation as it had during the Stuxnet computer virus outbreak believed to have been engineered by the US and Israel. Tehran's reaction so far shows Iranian officials are increasingly taking the possibility seriously.
"If it is proven that our country has been attacked by cyberattacks, we will respond," warned Gen Gholam Reza Jalali, the head of Iran's military unit in charge of combating sabotage, according to a report late on Thursday by the Mizan news agency.
Iran's Atomic Energy Organisation initially reported an "incident" had occurred early on Thursday at Natanz, located in the desert in the central province of Isfahan.
It later published a photo of a one-story brick building with its roof and walls partly burned. A door hanging off its hinges suggested there had been an explosion inside the building.
An article issued on Thursday by state news agency IRNA addressed what it called the possibility of sabotage by enemies such as Israel and the United States, although it stopped short of accusing either directly.
"So far Iran has tried to prevent intensifying crises and the formation of unpredictable conditions and situations," IRNA 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."
In 2010, the Stuxnet computer virus, which is widely believed to have been developed by the United States and Israel, was discovered after it was used to attack the Natanz facility.
Lukasz Olejnik, a Brussels-based independent cybersecurity researcher and consultant, said that incident did not necessarily say much about what transpired on Thursday.
Events taking place more than 10 years ago, and once, in themselves cannot form any evidence about things happening today, Olejnik, who formerly worked as scientific adviser on cyberwarfare at the International Committee of the Red Cross, said in an email.
He added that talk of a cyberattack was "way too premature and that invoking the specter of digital sabotage might be a convenient explanation for natural events, or incompetence.
Asked on Thursday evening about recent incidents reported at strategic Iranian sites, Israeli Prime Minister Benjamin Netanyahu told reporters: "Clearly we can't get into that."
The IAEA said on Friday the location of the fire did not contain nuclear materials, and that none of its inspectors was present at the time.
"The Agency has been in contact with relevant Iranian authorities to confirm there will be no impact on its safeguards verification activities, which are expected to continue as before," an IAEA statement said, adding that Iran had told it the cause of the fire was not yet known.
Natanz is the centrepiece of Iran's enrichment programme, which Tehran says is only for peaceful purposes. Western intelligence agencies and the IAEA believe it had a coordinated, clandestine nuclear arms programme that it halted in 2003.
Tehran denies ever seeking nuclear weapons.
Iran curbed its nuclear work in exchange for the removal of most global sanctions under an accord reached with six world powers in 2015, but has reduced compliance with the deal's restrictions since the United States withdrew in 2018.