an explosion in the Natanz nuclear plant in July. The explosives had been sealed inside a heavy desk that had been placed in the plant months earlier, Fereydoon Abbasi-Davani, the former chief of Iran’s Atomic Energy Organization, said.

The explosion ripped through a factory producing a new generation of centrifuges, setting back Iran’s nuclear enrichment program by months, officials said.

more recent explosion at Natanz this month except that it destroyed the plant’s independent power system, which in turn destroyed thousands of centrifuges.

It would have been difficult for Israel to carry out these operations without inside help from Iranians, and that may be what rankles Iran most.

execution.

But the infiltrations have also sullied the reputation of the intelligence wing of the Revolutionary Guards, which is responsible for guarding nuclear sites and scientists.

A former Guards commander demanded a “cleansing” of the intelligence service, and Iran’s vice president, Eshaq Jahangiri, said that the unit responsible for security at Natanz should be “be held accountable for its failures.”

The deputy head of Parliament, Amir-Hossein Ghazizadeh Hashemi, told the Iranian news media on Monday that it was no longer enough to blame Israel and the United States for such attacks; Iran needed to clean its own house.

As a publication affiliated with the Guards, Mashregh News, put it last week: “Why does the security of the nuclear facility act so irresponsibly that it gets hit twice from the same hole?”

But the Revolutionary Guards answer only to Iran’s supreme leader, Ayatollah Ali Khamenei, and so far there has been no sign of a top-down reshuffling.

After each attack, Iran has struggled to respond, sometimes claiming to have identified those responsible only after they had left the country or saying that they remained at large. Iranian officials also insist that they have foiled other attacks.

were arrested last month in Ethiopia for plotting to attack Israeli, American and Emirati targets.

But any overt retaliation risks an overwhelming Israeli response.

“They are not in a hurry to start a war,” said Talal Atrissi, a political science professor at the Lebanese University in Beirut. “Retaliation means war.”

Conversely, the timing of Israel’s latest attack on Natanz suggested that Israel sought if not to derail the talks, to at least weaken Iran’s bargaining power. Israel opposed the 2015 nuclear agreement and opposes its resurrection.

the covert, regionwide shadow war between Israel and Iran has intensified with Israeli airstrikes on Iranian-backed militias in Syria and tit for tat attacks on ships.

But as Iran faces a struggling economy, rampant Covid-19 infections and other problems of poor governance, the pressure is on to reach a new agreement soon to remove economic sanctions, said Ms. Vakil of Chatham House.

“These low-level, gray zone attacks reveal that the Islamic Republic urgently needs to get the J.C.P.O.A. back into a box” to free up resources to address its other problems, she said, referring to the nuclear deal, formally called the Joint Comprehensive Plan of Action.

Eric Schmitt contributed reporting from Washington, and Hwaida Saad from Beirut, Lebanon.

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