U.S. negotiators prepared to resume indirect talks with Iran this week in hopes that an attack on a key Iranian nuclear facility, widely attributed to Israel, would not derail the nascent effort at diplomacy.

Biden administration officials were quick to say the United States had nothing to do with the weekend incident, which caused a blackout that damaged centrifuges at the Natanz facility.

"The United States was not involved in any manner," White House press secretary Jen Psaki said Monday, and the administration has not been "given any indication about a change" in Iranian participation in negotiations over reviving the 2015 nuclear agreement among world powers and Iran that began last week in Vienna.

Other officials said there was no way to know how Iran would react until they return to the European Union-sponsored talks on Wednesday. After last week's initial meeting, both sides labeled the negotiations — held indirectly, with European members of the deal shuttling between U.S. and Iranian delegations — as constructive and businesslike. Iran has refused to meet directly with the United States.

Iranian officials across the board blamed Israel for the Natanz attack, which one called "nuclear terrorism" and a "crime against humanity."

But in an indication that Tehran wants the talks to continue, no public blame was directed at Washington, and there was no suggestion the discussions would halt.

"The Zionists want to take revenge on the Iranian people for their success in lifting the oppressive sanctions, but we will not allow it and we will take revenge on the Zionists themselves," Iranian Foreign Minister Javad Zarif said, according to the state-run Islamic Republic News Agency.

Israel, whose government staunchly opposes a U.S. return to the nuclear deal from which President Donald Trump withdrew three years ago, did not confirm or deny the accusations.

Yoel Guzansky, former head of the Iran desk at Israel’s National Security Council and a senior fellow at the Institute for National Security Studies, said Israeli media reports that Mossad, the Israeli spy agency, was involved in the Natanz blackout indicated a rare move to circumvent Israel’s military censor and unofficially claim responsibility.

“If it was authorized, Israel wants its name to be connected to the attack and to gain something, either vis-a-vis Iran or the U.S. If it’s unauthorized, it’s a security breach problem, but either way, it’s a problem,” he said. “It’s not healthy to brag, but you also force your opponent to do something, and I’m sure they will.”

There were differing versions of how the attack was undertaken, with reports of both a cyberattack and an explosion that destroyed the power transmission to the facility where Iran enriches uranium. Iran began increasing the quantity and quality of its enrichment far beyond the limits under the nuclear deal after Trump reimposed the sanctions lifted under the agreement and piled on more than 1,500 more in what his administration called a “maximum pressure” campaign to cripple the Iranian economy.

The Natanz incident potentially escalated a shadow war between Israel and Iran over the past several years, including increasingly publicized maritime attacks.

“In the Middle East, there is no threat that is more serious, more dangerous, more pressing than that posed by the fanatical regime in Iran,” Israeli Prime Minister Benjamin Netanyahu said during a Monday news conference with visiting U.S. Defense Secretary Lloyd Austin.

“Iran has never given up its quest for nuclear weapons and its missiles to deliver them,” Netanyahu said. Iran has said its nuclear program is intended for peaceful civilian purposes.

Austin, the first senior Biden administration official to visit Israel, avoided public discussion of the weekend attack. Instead, he said the purpose of the two-day trip was to “reaffirm the administration’s commitment to Israel and the Israeli people.”

“I wanted to underscore my personal pledge to strengthening Israel’s security and ensuring Israel’s qualitative military edge,” Austin said.

One Middle East official, speaking on the condition of anonymity about the sensitive situation, said the “objective of the operation was to buy time” for Israel as the Biden administration sets out its own posture toward the region. Many of its regional partners, including Israel and the Persian Gulf states, had close relationships with Trump and oppose any effort to lift the pressure he imposed on Iran.

The administration, while pledging support to Israel, is uncomfortable with many of Netanyahu’s policies. Its position on Iran, expressed by President Biden during his campaign and since his inauguration, is that the nuclear deal succeeded in curtailing Iran’s nuclear program. He has said that once the agreement — including Britain, France, Germany, Russia and China — is revived, he wants to open negotiations with Iran to lengthen and strengthen its original terms and address other complaints about Iranian behavior such as its ballistic missile program, proxy wars and alleged support for terrorism.

Iran has said it is not interested in follow-up talks and has demanded that the United States comply with its obligations under the deal and lift all sanctions before it will return to nuclear compliance. The purpose of the Vienna talks is to establish a road map under which the two sides will work out mutual, sequential steps.

In Europe, there was deep worry that the Natanz attack could sabotage their delicate work.

“We are following this very closely and with concern,” said Peter Stano, a spokesman for the European Commission, which is chairing the Vienna talks. “Any attempt to derail them, undermine them, has to be fully rejected. And all questions related to the Iranian nuclear program need to be resolved through diplomatic means because there is no other alternative, no sustainable alternative.”

No one presumes that the negotiations are on a glide path to success.

“These attacks are counterproductive from so many perspectives,” said one European diplomat familiar with the progress of the talks, who spoke on the condition of anonymity to discuss the tense situation. They empower Iranian hard-liners, who were always skeptical of the deal, and by feeding the narrative that the United States is subservient to Israeli interests, “this is also not helpful for the U.S.,” the diplomat said.

Although Iranian officials acknowledged that centrifuges were damaged, Ali Akbar Salehi, head of the Atomic Energy Organization of Iran, said Monday that emergency power systems were put into operation afterward and that “enrichment in Natanz has not stopped and is moving forward vigorously,” according to the IRNA.

In a news briefing Monday, Saeed Khatibzadeh, an Iranian Foreign Ministry spokesman, called the suspected attack on the Natanz site “a bold act of nuclear terrorism on Iranian soil” and among the “crimes against humanity which the Israeli regime has been doing for many years now.”

There were no casualties or nuclear contamination as a result of the attack, but it could have “resulted in a catastrophic situation,” he said.

Khatibzadeh added that some of the older-generation centrifuges were damaged but would be replaced by newer ones.

A catastrophic power outage carries at least a potential for inflicting substantial damage. The facility houses thousands of fast-spinning centrifuges — the machines at the core of the uranium enrichment process — and even a minor disruption can harm delicate internal components, nuclear experts said. In the early 2000s, as Iran was just beginning to enrich uranium, a sudden shutdown of an array of centrifuges caused irreparable damage to about a third of the machines involved, said David Albright, president of the Institute for Science and International Security, a Washington research organization that has tracked Iran’s nuclear activities for decades.

Iran’s eagerness to rebuild its economy — and the unease many other countries feel about the U.S. sanctions — was on display Monday during a visit to Tehran by South Korean Prime Minister Sye-kyun Chung, the first official South Korean trip there in decades.

Iran wants South Korea to release $7 billion in funds it has frozen under the sanctions, and Seoul has made clear that the United States asked it to hold back.

“I think that seeking a way to quickly return it [to Iran] is the right way to serve our national interest,” Chung told reporters traveling with him, according to South Korea’s semiofficial news wire service Yonhap. “That could not be realized due to several restraints, and thus we need to make more efforts from now on.”

Rubin reported from Tel Aviv, and Fahim reported from Istanbul. Paul Schemm in Dubai, Min Joo Kim in Seoul, Michael Birnbaum in St. Louis and Souad Mekhennet and Joby Warrick in Washington contributed to this report.