Iran warned Tuesday it will start enriching uranium up to 60 percent purity, two days after an explosion it blamed on Israel damaged its enrichment plant in Natanz.
The announcement cast a shadow over ongoing multinational talks in Vienna aimed at salvaging the tattered 2015 nuclear deal between Iran and world powers.
Tehran has written to the UN's International Atomic Energy Agency to announce "that Iran will start 60 percent enrichment," the state-run IRNA news agency reported.
Such a move would bring Iran closer to the 90 percent purity threshold for military use. Under the nuclear deal, Iran had committed to keep enrichment to 3.67 percent.
The news came two days after an explosion knocked out power at Iran's main nuclear facility of Natanz in central Iran which Iran blamed on its arch-enemy Israel and labelled an act of "terrorism".
Israel, which did not claim responsibility for the act of sabotage, is strongly opposed to US President Joe Biden's efforts to revive the nuclear agreement, which Donald Trump abandoned in 2018.
The accord between Iran and the UN Security Council's permanent members plus Germany promised Iran relief from punishing sanctions in return for agreeing to limits on its nuclear programme.
Iran has always denied it is seeking a nuclear bomb, while Israel has vowed it will stop the Islamic republic from ever building an atom bomb, which it considers an existential threat to the Jewish state.
- 'Bad gamble' -
The mysterious blast at Natanz has sharply heightened tensions between the two powers already engaged in a shadow war on lands and seas across the Middle East, with Iran on Monday vowing to take "revenge".
"If (Israel) thought that they can stop Iran from following up on lifting sanctions from the Iranian people, then they made a very bad gamble," Iranian Foreign Mohammad Javad Zarif warned.
Iran would make the enrichment plant "more powerful" by using advanced centrifuges, he added.
IRNA added that the Islamic republic will also add "1,000 centrifuges with 50 percent more capacity to the machines present in Natanz, in addition to replacing" the ones damaged during an attack on the nuclear facility.
According to Iran's English-language Press TV, the enrichment jump will start on Wednesday.
After talks with his visiting Russian counterpart Sergei Lavrov, Zarif also warned Israel's ally the United States it would gain no extra leverage in Vienna through "acts of sabotage" and sanctions.
"The Americans should know that neither sanctions nor acts of sabotage will give them negotiation tools and these acts will only make the situation more difficult for them," Zarif told a joint news conference.
The White House has denied all US involvement in the Natanz incident.
Unsourced Israeli media reports attributed it to Israeli security services.
The New York Times, quoting unnamed US and Israeli intelligence officials, also said there had been "an Israeli role" in the attack in which an explosion had "completely destroyed" the power system that fed the plant's "underground centrifuges".
Quoting another unnamed intelligence source on Tuesday, the NYT added an "explosive device had been smuggled" into the site and "detonated remotely," taking out primary and backup power.
- 'Worse than a crime' -
Lavrov, during his Tehran visit, stressed Russian support for Iran's position.
He said Moscow still expected Washington to return to the nuclear deal with Tehran, but criticised moves he said complicated the Vienna talks.
"We are counting on the fact that we will be able to save the agreement and that Washington will finally return to full and complete implementation of the corresponding UN resolution," Lavrov told the joint press conference.
Europe's "inability to implement" its nuclear deal commitments and "bowing to America's pressure" shows it is "slowly losing its relevance in international relations", Zarif said.
He also blasted the European Union for slapping sanctions on eight Iranian security officials, in response to a crackdown on 2019 street protests, saying that the blacklisting threatens efforts to restore the deal.
"If this decision was taken voluntarily in the midst of negotiations in Vienna ... then it is no longer unfortunate, it is a mistake worse than a crime," said Lavrov.
"I hope our European colleagues understand that such actions are unacceptable and will take measures not to allow the talks to be derailed."
Lavrov's remarks come at a time of heightened tensions between Russia and the West over various issues, including Ukraine.
Iranian President Hassan Rouhani told Lavrov that Iran expects a "return to 2015's agreements and obligations."
"We are neither ready to accept anything less than that nor seek to gain anything more," he said, according to a statement on his official website.
For now, the agreement remains in limbo with neither Tehran nor Washington backing down from their positions, and each demanding the other make the first move.