Iran blames regional arch-foe Israel for a sabotage incident at its key Natanz nuclear site and will exact revenge, state TV quoted its foreign minister as saying, in what appeared to be latest episode in a long-running covert war.

Iran’s semi-official Nournews website said the person who caused an electricity outage in one of the production halls at the underground uranium enrichment plant had been identified. “Necessary measures are being taken to arrest this person,” the website reported, without giving details about the person.

The incident occurred amid diplomatic efforts by Iran and the United States to revive Tehran’s 2015 nuclear deal with major powers, an accord Israel fiercely opposed, after former U.S. President Donald Trump abandoned it three years ago.

Last week, Iran and the global powers held what they described as “constructive” talks to salvage the deal, which has unravelled as Iran has breached its limits on sensitive uranium enrichment since Trump reimposed harsh sanctions on Tehran.

Iranian authorities described the incident a day earlier as an act of “nuclear terrorism” and said Tehran reserved the right to take action against the perpetrators.

On Monday, Foreign Minister Mohammad Javad Zarif explicitly blamed Israel. “The Zionists want to take revenge because of our progress in the way to lift sanctions…They have publicly said that they will not allow this. But we will take our revenge against the Zionists,” Zarif was quoted by state TV as saying.

Multiple Israeli media outlets have quoted unnamed intelligence sources as saying the country’s Mossad spy service carried out a successful sabotage operation at the underground Natanz complex, potentially setting back enrichment work there by months. Israel has not formally commented on the incident.

ADVANCED CENTRIFUGES

The incident took place a day after Tehran, which has insisted it wants only peaceful nuclear energy not nuclear weapons, started new advanced enrichment centrifuges at Natanz.

Iranian Foreign Ministry spokesman Saeed Khatibzadeh told a news conference on Monday that the incident could be deemed an “act against humanity”, adding it had caused “no contamination or casualties” at the site.

“Our nuclear experts are assessing the damage but I can assure you that Iran will replace damaged uranium enrichment centrifuges in Natanz with advanced ones,” Khatibzadeh said.

The incident also coincided with a visit to Israel by U.S. Secretary of Defense Lloyd Austin, who pledged the Biden administration’s support for its Middle East ally.

“I’m committed to continuing our close consultations on threats posed by Iran and to strengthening Israel’s security,” Austin tweeted late on Sunday.

A senior U.S. administration official said Washington had no involvement in the incident. “We have nothing to add to speculation about the causes,” the official said.

At a ceremony on Sunday, Israeli Prime Minister Benjamin Netanyahu made no direct reference to Natanz, though said: “The fight against Iran’s nuclearisation…is a massive task.”

There have been sporadic incidents of sabotage and outages at Iranian nuclear installations for over a decade, for which Tehran has blamed Israel, which regards the Iranian nuclear programme as a menace to its existence.

In 2010, the Stuxnet computer virus, widely believed to have been developed by the United States and Israel, was discovered after it was used to attack Natanz, causing damaging breakdowns of centrifuge cascades that refine uranium.

In July last year, a fire broke out at Natanz that Iran said was an attempt to sabotage its enrichment activity.

Iran also blamed Israel for last November’s assassination of Mohsen Fakhrizadeh, who was seen by Western intelligence services as the mastermind of a covert Iranian nuclear weapons programme. Israel has neither confirmed nor denied responsibility for the killing.