The European countries party to the Iran nuclear deal told Tehran on Wednesday that its decision to enrich uranium to 60 per cent purity, bringing it closer to that needed for a bomb, went against efforts to revive the accord.
But in an apparent signal to Israel, which Tehran blamed for an explosion at its key nuclear site on Sunday, Germany, France and Britain said they rejected "all escalatory measures by any actor".
Israel, which Iran does not recognise, has not formally commented on the incident at Iran's Natanz site, which appeared to be the latest twist in a long-running, covert war.
The 2015 nuclear deal has unravelled as Iran breached its limits on uranium enrichment in a phased response to the US withdrawal from the agreement in 2018 and reimposition of harsh economic sanctions.
Last week, Iran and fellow signatories held "constructive" talks to restore the deal from which the former Trump administration withdrew, saying its terms were too lenient on Tehran.
The decision to pull out of the agreement was welcomed by Israel.
US President Joe Biden's administration and Iran will reconvene indirect talks on Thursday in Vienna, White House press secretary Jen Psaki said.
But Britain, France and Germany said Tehran's decision to enrich at 60 per cent, and activate 1,000 advanced centrifuges at its Natanz plant, was at odds with the talks.
They said it was not based on credible civilian reasons and was an important step towards the production of a nuclear weapon.
"Iran's announcements are particularly regrettable given they come at a time when all [nuclear deal] participants and the United States have started substantive discussions" to return to the agreement, the three countries said.
"Iran’s dangerous recent communication is contrary to the constructive spirit and good faith of these discussions."
The talks resume between Iran and global powers in Vienna on Thursday.
Later on Wednesday, Iranian supreme leader Ayatollah Ali Khamenei said the US was trying to impose its terms for rescuing the deal and European powers were doing Washington's bidding.
"America does not seek to accept the truth in negotiations," Mr Khamenei, who has the last word on matters of state, told local TV.
"Its goal in talks is to impose its own wrong wishes ... European parties to the deal follow America's policies in talks despite acknowledging Iran’s rights.
"The nuclear talks in Vienna must not become talks of attrition. This is harmful for our country."
Mr Biden took office in January with a commitment to rejoin the deal if Tehran returns to full compliance with its restrictions on enrichment.
Tehran has repeatedly said that all sanctions must be rescinded first.
"We have already declared Iran's policy. Sanctions must be removed first," Mr Khamenei told the semi-official Tasnim news agency.
"Once we are certain that has been done, we will carry out our commitments.
"The offers they provide are usually arrogant and humiliating, and are not worth looking at."
Iran has "almost completed preparations" to begin 60 per cent enrichment.
It has notified the International Atomic Energy Agency that it will activate 1,024 more IR-1 centrifuges, its older first generation of the machines, the UN nuclear watchdog said on Wednesday.
The White House called Iran's 60 per cent enrichment announcement "provocative" and said it was concerned.
Referring to the Natanz blast and Iran's response, the European countries said: "In light of recent developments, we reject all escalatory measures by any actor, and we call upon Iran not to further complicate the diplomatic process."
Saudi Arabia on Wednesday said it believed any revival of the nuclear deal should be a starting point for further talks, which include regional states, to expand the accord.
Any deal that fails to address the security concerns of countries in the region would not work and Riyadh was consulting with the global powers, Rayd Krimly, head of policy planning at the Saudi Foreign Ministry, told Reuters.
"We want to make sure at a minimum that any financial resources made available to Iran via the nuclear deal are not used ... to destabilise the region," Mr Krimly said.
Iran’s deal with the six powers limits the purity to which it can refine uranium at 3.67 per cent.
That is well under the 20 per cent achieved before the agreement, and far below the 90 per cent suitable for a nuclear weapon.
