Iran's 2020 Explosions: What Happened at Natanz and Beyond

Originally published 2020-07-06.

Between late June and mid-July 2020, Iran saw an unusual run of blasts, fires and leaks at military, industrial and civilian sites. The most serious was a fire and explosion on 2 July at the centrifuge assembly building of the Natanz enrichment site, Iran's most important nuclear facility. Iranian officials acknowledged significant damage, and outside analysts estimated it set back work on advanced centrifuges by one to two years.

No government formally claimed any of the incidents. Some were plainly accidents in an ageing industrial sector during a hot summer; others, above all Natanz, were widely viewed as sabotage. Here is what happened, who was blamed, and why the episode mattered.

The incidents, in order

The sequence began on 25 June 2020, when a large blast lit up the night sky east of Tehran near the Parchin military complex. Officials said a gas storage tank had exploded; satellite images examined by outside analysts reportedly pointed to an area near the Khojir missile production site. Within the same hour, part of the southern city of Shiraz lost power after what officials described as an explosion at a power station.

Another video. pic.twitter.com/f7goYoMkNQ

— Farnaz Fassihi (@farnazfassihi) June 25, 2020

(This post is no longer available on X.)

Five days later, on 30 June, an explosion at the Sina At'har clinic in northern Tehran killed 19 people, most of them women. City officials blamed leaking medical gas canisters. This was a civilian tragedy with a plausible ordinary cause, but it landed in the middle of the wider pattern and fed public anxiety.

Then came Natanz on 2 July. In the following days there were further reports: a fire and explosion at the Shahid Medhaj (Zargan) power plant near Ahvaz and a chlorine gas leak at the Karun petrochemical plant in Mahshahr on 4 July, which injured around 70 workers; an explosion at an oxygen factory south of Tehran on 7 July that killed two people; and further fires at petrochemical plants, a pipeline and industrial units through the rest of July.

Accident or attack?

Not every incident on that list deserves the label "mysterious". Iran has a long record of industrial accidents linked to old equipment, gas leaks and lax safety. Several events, such as a residential gas explosion in Tehran, almost certainly had nothing to do with foreign interference. Grouping them all together made the summer look more coordinated than the evidence supports.

What happened at Natanz

The Natanz fire broke out around 2am on 2 July 2020 in an above-ground building where Iran assembled advanced centrifuges, the machines that spin uranium gas to enrich it. The main enrichment halls at Natanz are deep underground and were not hit. Photographs released by Iran's Atomic Energy Organization showed a scorched, partly collapsed structure with blown-out doors and a blackened roof.

IRIB is now broadcasting footage of the spokesman of #Iran’s Atomic Energy Organization giving a tour of the wreckage from the incident at #Natanz. 1/2 pic.twitter.com/zk9b6HK2zg

— Jason Brodsky (@JasonMBrodsky) July 2, 2020

At first the Atomic Energy Organization spoke of an "incident" and an accident under investigation. Within a day, three Iranian officials told Reuters anonymously that they believed it was a cyber attack, though they offered no proof. A Middle Eastern intelligence official later told the New York Times that an explosive device was to blame. Later in 2020, Iranian nuclear officials said security investigators had concluded that it was sabotage.

The location made coincidence hard to believe. Fabian Hinz, a researcher at the James Martin Center for Nonproliferation Studies, put it plainly to reporters: a fire in such a building is possible, but he found it striking that "it's this one, very sensitive building that catches fire or explodes."

The International Atomic Energy Agency later reported that Iran had begun building a new centrifuge assembly plant inside a mountain near Natanz to replace the damaged one, a sign that Tehran saw the building as a target.

Who claimed responsibility, and who Iran blamed

Shortly after the Natanz fire, a previously unknown group calling itself the "Cheetahs of the Homeland" (also translated as Homeland Panthers) reportedly sent a statement to Persian-language media abroad, including Radio Farda, saying it had carried out the attack. It described itself as a network of dissidents inside Iran's security forces. No one has been able to verify its existence, and several analysts suspected the claim was a cover story for a foreign operation.

Iranian officials instead pointed to their long-standing adversaries. Through the state news agency IRNA, the government warned that if hostile countries, which it named as Israel and the United States, crossed its "red lines", its policy of restraint would have to change. Israeli officials, true to a long habit of ambiguity, neither confirmed nor denied involvement. US and Israeli officials told the New York Times they had nothing to do with the Parchin blast.

Background: a long shadow war

The events make more sense against the history of the dispute over Iran's nuclear programme. Tehran says it wants nuclear technology for electricity and medicine. Israel, the United States and several European governments have long feared that enrichment could give Iran the material for a weapon. In 2018 the US withdrew from the 2015 nuclear deal (the JCPOA), and Iran then gradually increased enrichment beyond the deal's limits.

Tensions were already high in 2020. In January a US drone strike in Baghdad killed General Qasem Soleimani, commander of the Revolutionary Guards' Quds Force. Iran answered with ballistic missile strikes on Iraqi bases hosting US troops, including Ain al-Asad. Over the previous decade several Iranian nuclear scientists had been assassinated, attacks Iran blamed on Israel.

Stuxnet and cyber sabotage

Natanz had been a target before. In June 2010 a Belarusian security firm identified Stuxnet, a highly sophisticated computer worm built to sabotage the industrial controllers that ran Natanz's centrifuges. Multiple news organisations have reported that it was developed jointly by the United States and Israel under a programme code-named Olympic Games; neither government has admitted it. The Institute for Science and International Security estimated that up to 1,000 centrifuges, about a tenth of those installed, may have been destroyed.

Older versions of this story sometimes mix up the names. "Nitro Zeus" was a separate, much larger US contingency plan for cyber attacks on Iranian infrastructure if war broke out, revealed in Alex Gibney's 2016 documentary Zero Days. In the same film, anonymous US sources suggested Israel had modified the worm and made it more aggressive, which helped it spread beyond Natanz and get discovered.

What came after

The summer of 2020 turned out to be one chapter in a longer campaign. In November 2020 Mohsen Fakhrizadeh, the scientist seen as the father of Iran's military nuclear research, was killed in an ambush outside Tehran. In April 2021 a power failure and explosion hit Natanz again, a day after Iran started feeding gas into new advanced centrifuges. Iran blamed Israel and later named an Iranian suspect who, it said, had fled abroad.

Open conflict eventually replaced deniable sabotage. In June 2025, during the twelve-day war between Israel and Iran, Israeli strikes destroyed the pilot enrichment plant at Natanz, and US B-2 bombers then dropped bunker-buster bombs on the site. The IAEA later reported direct impacts on the underground halls.

How to read events like these

• Separate claims from evidence. A statement from an unknown group and an accusation from a government are both claims. Neither proves who caused an explosion.
• Look for official technical detail. Satellite images, IAEA reports and later admissions by officials tend to be more reliable than first-day reports.
• Don't force a pattern. A string of incidents in a short period can include genuine accidents. Natanz stands out precisely because the target was so specific.
• Expect silence. States conducting sabotage rarely confirm it. Attribution often rests on anonymous officials, so treat it with care.

What is not in doubt is that the Natanz blast was a serious setback to Iran's centrifuge programme and a clear escalation in a conflict that, five years later, broke into open war.

Sources: Wikipedia: 2020 Iran explosions; Wikipedia: Natanz Nuclear Facility; Wikipedia: Stuxnet; Middle East Center for Reporting and Analysis: Natanz explosion timeline; videos via X posts by Farnaz Fassihi and Jason Brodsky.