Iran said saboteurs caused a blackout at the country’s main nuclear-enrichment plant, accusing the alleged culprits of attempting to derail informal talks with the U.S. on reviving a 2015 nuclear accord that could pave the way for rolling back sanctions on the Islamic Republic. Tehran didn’t disclose any details about the electrical malfunction at Natanz, which it said took place Sunday, or the extent of any damage it caused. Nor did Iranian authorities say who they thought might be responsible, though Ali Akbar Salehi, the head of Iran’s atomic agency, said Iran reserved the right to retaliate. He called the incident an act of “nuclear terrorism” amid heightened tensions over the tentative discussions on Iran’s nuclear program.

Israeli media, quoting what they described as Western intelligence sources, said Israeli intelligence agency Mossad had orchestrated a cyberattack at the Natanz site, causing severe damage.

Israeli officials declined to respond to the reports that Israel was behind the alleged attack at Natanz. In Washington, a spokeswoman for the White House National Security Council declined to comment.

Iran and the remaining five parties to the 2015 nuclear accord converged in Vienna last week to negotiate a road map for the U.S. to return to the agreement, which the Trump administration left in 2018. Their objective is to find a way for President Biden’s administration to lift sanctions on Iran if Tehran agrees to comply with the 2015 pact, which was developed to curtail the growth of Iran’s nuclear capability, and keep it from developing nuclear-weapons technology.

Iran ramped up its nuclear activities after the U.S. left the accord, including moves to enrich uranium at a higher purity than the deal allows. Natanz is at the center of Iran’s efforts, and was relaunched Saturday after a devastating explosion and fire in the summer of 2020, which Iran also blamed on saboteurs. Iran on Saturday carried out tests on a new generation of centrifuges.

Amos Yadlin, the former chief of Israeli military intelligence, however said in an interview with the country’s Army Radio Sunday that Israel may be pursuing short-term goals without considering the longer-term impact they may have on relations with the U.S.

“Are these things being considered extensively? I’m not convinced,” Mr. Yadlin said.

Iran insists that its nuclear program is peaceful. Its diplomats say they worry that Israel might take action to undermine the nuclear talks if it senses that they might undermine its own security.

Tehran’s announcement of the incident at Natanz, in the center of Iran, came as U.S. Defense Secretary Lloyd Austin landed in Tel Aviv for meetings with Mr. Netanyahu and other top Israeli officials, who were quick to raise the topic of Iran and the nuclear talks in Vienna.

“The Tehran of today poses a strategic threat to the world,” Israeli defense minister Benny Gantz said in a joint news conference with Mr. Austin. “We will work with our ally in the U.S. to ensure that any agreement protects the vital interests of the international community, prevents an arms race, and contributes to Israeli security.”