ISTANBUL — Iran will begin enriching uranium to 60 percent purity, a top official said Tuesday, far exceeding its current level, in a defiant move following an attack on one of its key nuclear sites, Iranian news agencies reported.

Iran’s state-run Press TV quoted Iran’s lead nuclear negotiator, Abbas Araghchi, as saying the country informed the International Atomic Energy Agency of plans to start 60 percent uranium enrichment.

The announcement puts Iran closer to weapons-grade levels of more than 90 percent enrichment and exceeds its current top level of 20 percent.

The move adds another major hurdle to negotiations to revive a 2015 nuclear deal negotiated between Iran and six world powers.

Talks were set to reconvene in Vienna later this week between Tehran and the world powers, including the United States. Iran began breaching the accord after President Donald Trump withdrew from the deal in 2018, reimposed the sanctions on Tehran that were lifted under the agreement, and added more than 1,500 additional measures in what his administration called a “maximum pressure” campaign to cripple the Iranian economy.

Iran, in response, increased enriched uranium from the 3.67 percent purity stipulated by the deal to 20 percent.

After an initial meeting last week, both Tehran and Washington characterized the negotiations — held indirectly, with European members of the deal shuttling between U.S. and Iranian delegations — as constructive. Iran has refused to meet directly with the United States.

White House press secretary Jen Psaki on Tuesday called Iran’s vow to increase enrichment “provocative” and said it “calls into question Iran’s seriousness with regard to the nuclear talks.”

Iran’s announcement follows an attack on its main enrichment facility at Natanz on Sunday, in what appeared to be an escalation of a shadow war between Israel and Iran over the past several years. There were differing versions of how the attack was carried out, with reports of both a cyberattack and an explosion that destroyed power transmission and caused a fire. Iranian officials blamed Israel for the attack, which they said caused a blackout and damaged centrifuges.

Israel has not publicly commented.

The Biden administration quickly said the United States had nothing to do with the incident, which Iran seemed eager to use as leverage in the Vienna negotiations.

In his comments Tuesday, Araghchi said another 1,000 centrifuges with 50 percent more capacity would be deployed at Natanz, in addition to the replacement of the damaged centrifuges.

The attack laid bare the abundance of obstacles facing diplomats in Vienna, aside from the complicated thicket of issues at the heart of the talks. Negotiators are concerned that Iran’s upcoming election in June will probably usher in a hard-line government that may be less disposed to dealmaking.

Now the events of recent days have added fears of a spiraling and incendiary conflict between Iran and Israel, which is opposed to the 2015 nuclear deal.

Last week, as the Vienna talks got underway, an Iranian ship in the Red Sea was crippled by an explosion that Iranian officials said was caused by mines. Then came Sunday’s attack on the Natanz nuclear facility.

And on Tuesday, the Hyperion Ray, a ship owned by an Israeli business executive, was struck by a missile in the Persian Gulf, according to Israel’s Channel 12 news, which quoted an unnamed Israeli defense official saying the attack was Iran’s first response to the incident at Natanz. Iran had no immediate comment on the reported ship incident.

The ship, which sails under the flag of the Bahamas, was only lightly damaged and would dock in the United Arab Emirates for repairs, the channel reported.

“The Natanz incident demonstrates in clear terms that spoilers are intent on disrupting talks aimed at reviving U.S.-Iran diplomacy,” said Suzanne DiMaggio, a senior fellow at the Carnegie Endowment for International Peace. “A dangerous, escalatory cycle is in play.”

The longer it takes to reach an agreement in Vienna on how to return to the deal, she said, the more the likelihood of derailment increases. Washington needs to be clear about what sanctions it is willing to lift, while Tehran needs to drop objections to direct talks, she said.

“Indirect talks have provided a way to get this process started, but direct diplomacy will be required to reach a sustainable agreement,” she said.

Iran’s announcement Tuesday drew immediate concern from European officials preparing to sit down again with Iranian negotiators later this week in Vienna. Talks that were planned for Wednesday were pushed back a day after a person in the E.U. entourage contracted the coronavirus.

A senior European diplomat familiar with the negotiations said the Iranian move was a major escalation that had the potential to derail the talks, since the intended level of enrichment strayed well into the realm of military use.

“When you are negotiating, there are some basic principles. One is that you negotiate in good faith. Another is you don’t escalate, you don’t change the basis of the negotiations,” said the diplomat, who spoke on the condition of anonymity to discuss the ongoing talks.

The nuclear deal allows Iran to enrich uranium only up to a 3.67 percent concentration of uranium-235, a fissile isotope, at Natanz, and to maintain a small stockpile of enriched uranium to use as fuel for its nuclear power reactors. Uranium enriched to 20 percent U-235 is suitable for use in an old, U.S.-supplied research reactor in Tehran that began operating in 1967.

Iran has repeatedly insisted that its nuclear program is intended for peaceful civilian purposes. On Tuesday, the U.S. intelligence community reported that Iran “is not currently undertaking” key activities necessary to produce a nuclear weapon. The finding, which was part of the intelligence agencies’ Annual Threat Assessment, affirmed an earlier judgment by the spy agencies.

The U.S. intelligence report had cited enrichment above 60 percent as a step Iran might take in developing nuclear weapons if it did not receive sanctions relief. In February, Iran’s supreme leader, Ayatollah Ali Khamenei, warned that Iran might take such a step and portrayed it as a sovereign right.

Iran would increase its uranium enrichment to “whatever level the country needs,” he said.

Mehrzad Boroujerdi, director of the School of Public and International Affairs at Virginia Tech, said Tehran may try to keep the tit-for-tat conflict with Israel under the threshold that triggers a conflict, while keeping its eyes on the “major prize” of lifting sanctions through negotiations in Vienna.

But both Iran and Israel have domestic considerations that could complicate the picture for negotiators, including the Iranian elections.

Israeli Prime Minister Benjamin Netanyahu, who has resisted calls to step aside as he faces corruption charges, is eyeing a fifth election in two years after failing to win enough of the vote to form a government in the last four polls.

“He might be more prone to continue with such attacks,” said Boroujerdi, referring to the suspected Israeli roles in Natanz and the mine blast that hit the Iranian ship in the Red Sea.

“At some point the White House needs to decide whether they want to allow Israel to torpedo everything that they want to do with Iran, or not.”

Morris reported from Washington. Shira Rubin in Tel Aviv, Shane Harris in Washington and Michael Birnbaum in St. Louis contributed to this report.