Iran has started the process of enriching uranium to 60 percent fissile purity at an above-ground nuclear plant at Natanz, the UN nuclear watchdog said on Saturday, confirming earlier statements by Iranian officials.
The move has complicated talks aimed at reviving Iran's nuclear deal with major powers as it is a big step towards producing weapons-grade uranium.
Iran had previously only reached 20 percent purity, and that was already a breach of the deal, which says Iran can only enrich to 3.67 percent.
Iran made the step up to 60 percent in response to an explosion that damaged equipment at the larger, underground Fuel Enrichment Plant at Natanz. Tehran has blamed Israel and named a man wanted in connection with the blast.
"The Agency today verified that Iran had begun the production of UF6 enriched up to 60 percent... at the (above-ground) Natanz Pilot Fuel Enrichment Plant," the International Atomic Energy Agency said in a statement.
UF6 is uranium hexafluoride, the form in which uranium is fed into centrifuges for enrichment.
A confidential IAEA report to member states seen by Reuters provided more details.
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"According to Iran's declaration to the Agency, the enrichment level of the UF6 produced at PFEP was 55.3 percent U-235. The Agency took a sample of the produced UF6 for destructive analysis to independently verify the enrichment level declared by Iran. The results of this analysis will be reported by the Agency in due course," the report said.
On Friday, U.S. President Joe Biden called Tehran's enrichment move unhelpful but said he is pleased it is still in indirect talks with Washington about both countries resuming compliance with the 2015 nuclear deal.
"We do not support and do not think it's at all helpful that Iran is saying it's going to move to enrich to 60 percent," Biden told reporters in Washington during a joint news conference with Japanese Prime Minister Yoshihide Suga.
"We are, though, nonetheless pleased that Iran has continued to agree to engage in discussions – indirect discussions – with us and with our partners on how we move forward and what is needed to allow us to move back into the (nuclear deal) ... without us making concessions that we are just not willing to make," Biden added.
A 2015 deal with world powers to rein in Iran's nuclear ambitions in return for the lifting of sanctions had capped the level of purity at 3.67 percent. Iran denies seeking a nuclear weapon.
Iran and global powers met in Vienna on Saturday to try to rescue the 2015 nuclear deal abandoned by former U.S. President Donald Trump three years ago – an effort potentially complicated by Tehran's decision to ramp up uranium enrichment.
"We have this (Iranian) decision to go for 60 percent enrichment. Obviously this is not making the negotiation easier," an EU official told reporters, calling what happened at Natanz "deliberate sabotage".
Abbas Araqchi, Iran's chief negotiator at the talks, said on Tuesday that Iran would activate 1,000 advanced centrifuge machines at Natanz.
Multiple Israeli media outlets have quoted unnamed intelligence sources as saying the country's Mossad spy service carried out the sabotage operation at the Natanz complex. Israel has not formally commented on the incident.