Iran mentioned Tuesday that it will start enriching uranium to a stage of 60 p.c purity, thrice the present stage and far nearer to that wanted to make a bomb, although American officers doubt the nation has the power to supply a weapon within the close to future.

Deputy Overseas Minister Seyed Abbas Araghchi, Iran’s high nuclear negotiator, didn’t give a cause for the shift, but it surely seemed to be retaliation for an Israeli assault on Iran’s major nuclear gasoline manufacturing plant in addition to a transfer to strengthen Iran’s hand in nuclear talks in Vienna.

Mr. Araghchi mentioned that Iran had knowledgeable the Worldwide Atomic Power Company of its choice in a letter on Tuesday.

Iran additionally attacked an Israeli-owned cargo ship off the coast of the United Arab Emirates on Tuesday, officers mentioned, the most recent conflict in its maritime shadow war with Israel. The assault was one other signal of elevated tensions within the area however was reported to have precipitated little to no harm.

The uranium enrichment announcement got here as American intelligence companies mentioned that whereas Iran had progressively resumed manufacturing of nuclear materials since President Donald J. Trump withdrew from the 2015 nuclear accord, there was no proof it had resumed the work wanted to style that materials right into a nuclear weapon.

“We proceed to evaluate that Iran will not be at the moment endeavor the important thing nuclear weapons-development actions that we decide can be needed to supply a nuclear machine,’’ the companies mentioned of their annual threat assessment report launched on Tuesday.

The report mentioned, nonetheless, that “if Tehran doesn’t obtain sanctions aid” — as Iran has demanded — “Iranian officers in all probability will think about choices starting from additional enriching uranium as much as 60 p.c to designing and constructing a brand new” nuclear reactor that might, over the long run, produce bomb-grade materials. That might take years.

The evaluation would appear to present President Biden some respiration room as he enters negotiations in Vienna aimed toward restoring some type of the nuclear settlement.

However there are nonetheless dangers: Iran has a protracted relationship with North Korea, with which it has exchanged missile know-how, and officers have for years been involved that Iran would possibly search to purchase confirmed nuclear-weapons know-how from the North.

The White Home press secretary, Jen Psaki, referred to as Iran’s announcement on Tuesday “provocative,” and mentioned it “calls into query Iran’s seriousness regarding the nuclear talks.”

Mr. Araghchi, who was deeply concerned in negotiating the 2015 nuclear accord between Tehran and the US, additionally mentioned Tuesday that Iran would change the centrifuges broken by the attack on Sunday on the nuclear fuel-production heart at Natanz, the place an explosion knocked the power offline. He mentioned that Iran would set up an extra 1,000 centrifuges there to extend the plant’s capability by 50 p.c.

An Iranian official additionally offered a brand new estimate of the harm attributable to the assault, saying that a number of thousand centrifuges have been “fully destroyed.” That stage of destruction takes out a big portion of Iran’s means to complement uranium.

However the full extent of the harm is unknown, and Iran presumably is susceptible to continued assaults on its nuclear infrastructure. Till the electrical energy techniques are rebuilt at Natanz, it will be unimaginable to make new centrifuges spin.

Iran is anticipated to switch the first-generation centrifuges broken within the Israeli assault with extra superior, extra environment friendly fashions.

Iran has one other recognized manufacturing facility, Fordow, buried deep inside a mountain, however its capability is restricted.

Iran blamed Israel for the explosion at Natanz on Sunday, an evaluation confirmed by American and Israeli intelligence officers. The Israeli authorities has not commented publicly.

Mr. Araghchi is in Vienna this week for oblique talks with the US to revive the 2015 nuclear deal. The deal put restrictions on Iran’s nuclear program in change for the lifting of sure sanctions on Iran, and Mr. Biden has advocated restoring it in some method.

After the US withdrew from the deal and Mr. Trump imposed new sanctions, Iran deserted its commitments below the settlement and elevated its enrichment of uranium to twenty p.c, a stage that may have violated the phrases of the accord.

Uranium enriched to 60 p.c purity can be an additional violation, and is a brief step from bomb gasoline, which is usually thought-about 90 p.c or greater in purity. Whereas uranium enriched to 60 p.c can be utilized as gasoline in civilian nuclear reactors, such functions have been discouraged globally as a result of it may so simply be become bomb gasoline.

Iran has been enriching uranium to roughly 20 p.c purity at its Fordow plant, which uses about 1,000 centrifuges.

To boost the extent to 60 p.c purity, Iran must flip over roughly half of these machines onto the brand new enrichment job. Purifying it to 90 p.c would require one other hundred or so machines.

In an interview, Olli Heinonen, a former chief inspector for Worldwide Atomic Power Company, based mostly in Vienna, mentioned that theoretically Iran may go from 60 p.c to 90 p.c enrichment in every week, in contrast with a month or so ranging from 20 p.c.

“It’s not an enormous distinction,” he mentioned.

“At this level, this can be a demonstration,” Dr. Heinonen mentioned of Iran attaining the 60 p.c stage. “They need to present that they will do it.”

The rather more tough step, he mentioned, can be turning uranium enriched to 90 p.c into the core of an atom bomb.

In one other attainable retaliation for the Israeli assault on Sunday, Iran attacked an Israeli-owned cargo ship, the Hyperion Ray, off the coast of the United Arab Emirates, on Tuesday.

In response to an individual acquainted with the main points of the ship’s voyage, the ship evaded the assault and was not hit. Israeli information media reported that it suffered mild harm.

An Israeli safety official mentioned that Israel was searching for to scale back tensions within the Persian Gulf area and that it had no intention of responding with one other assault on an Iranian vessel.

The Israeli Military, the Protection Ministry and the prime minister’s workplace all declined to remark.

In current days, Israel had requested the US for assist defending the ship, an American official mentioned.

Israeli officers have been involved that it might be focused by Iran’s Islamic Revolutionary Guards Corps in response to final week’s apparent mine attack by Israel on an Iranian army vessel within the Purple Sea, the American official mentioned.

A cargo ship owned by the identical firm, the Helios Ray, was attacked by Iran earlier this 12 months.

Iranian officers additionally revealed extra particulars concerning the Natanz assault on Tuesday, suggesting that the harm was better than Iran beforehand reported.

Alireza Zakani, a member of Parliament and head of its analysis heart, mentioned on state tv that “a number of thousand of our centrifuges have been fully destroyed,” representing a big portion of the nation’s means to complement uranium.

He described official statements on Monday that the power can be shortly repaired as false guarantees.

Overseas intelligence officers have mentioned it may take many months for Iran to undo the harm.

Iranian officers have been furious concerning the safety lapses which have allowed a sequence of assaults on Iran’s nuclear program over the previous 12 months, starting from sabotage of nuclear services to the theft of labeled paperwork to the assassination of Iran’s chief nuclear scientist. Most of those assaults have been presumed to have been carried out by Israel.

Mr. Zakani criticized Iran’s safety equipment as lax, saying it had allowed spies to “roam free,” turning Iran into “a haven for spies.”

He mentioned that in a single incident, some nuclear gear belonging to a significant facility was despatched overseas for restore and that when it returned the gear was filled with 300 kilos of explosives. In one other incident, he mentioned, explosives have been positioned in a desk and smuggled contained in the nuclear facility.

Iran has lengthy maintained that its nuclear program is peaceable and aimed toward vitality growth. Israel claims that Iran had and should have an energetic nuclear weapons program and considers the potential for a nuclear-armed Iran an existential risk.

The nuclear talks that started in Vienna final week have been delayed as a result of a member of the European Union delegation examined constructive for the coronavirus. The talks may resume as early as Thursday if the member exams unfavorable.

Patrick Kingsley, Ronen Bergman and Steven Erlanger contributed reporting.