Almost half of Iran's uranium enriched to up to 60 per cent purity, a short step from weapons-grade, was stored in a tunnel complex at Isfahan and is probably still there, UN nuclear watchdog chief Rafael Grossi has said.
The tunnel complex is the only target that appears not to have been badly damaged in attacks last June by Israel and the US on Iran's nuclear facilities.
Isfahan has been used to store substantial amounts 60 per cent uranium, which the International Atomic Energy Agency confirmed in a report to member states last month, without saying how much was there.
The IAEA estimates that when Israel launched its first attacks in June 2025, Iran had 440.9kg of 60 per cent uranium kept at nuclear plants nationwide. The agency tracked a convoy removing what was thought to be a substantial amount from another site – Fordow – shortly before last year's 12-day aerial war. Another batch of the enrichment material is believed to be stored at the Natanz nuclear plant. Only a short cycle of further enrichment is necessary to provide the explosive feedstock needed for 10 nuclear weapons, according to an IAEA yardstick.
“What we believe is that Isfahan had until our last inspection a bit more than 200kg, maybe a little bit more than that, of 60 per cent uranium,” IAEA chief Rafael Grossi said.
No transfer
Most of Iran's overall stock was kept at Isfahan and some held elsewhere may have been destroyed, he added.
“The widespread assumption is that the material is still there,” Mr Grossi said. “So we haven't seen – and not only us, I think in general all those observing the facility through satellite imagery and other means to see what's going on there – movement indicating that the material could have been transferred.”
Iran has not informed the IAEA of the status or whereabouts of its highly enriched uranium since the attacks last June, nor has it let the UN's nuclear inspectors return to its bombed facilities.
Iran's nuclear programme is one reason Israel and the US have given for their current attacks, arguing that the regime was getting too close to being able to produce a bomb, despite US President Donald Trump saying that last summer's US strikes had obliterated the entire atomic project. The IAEA has said it had no credible indication of a co-ordinated nuclear weapons programme.
All three – two at Natanz and one at Fordow – of Iran's then active uranium-enrichment plants, known to IAEA inspectors, were destroyed or badly damaged in June. “There is an amount [of 60 per cent uranium] in Natanz also, which we believe is still there,” Mr Grossi said.
The only solution to Iran's nuclear programme is diplomacy, Mr Grossi told French radio station RFI. “We will have to return to the negotiating table and find a lasting solution to this conflict that has affected us for 20 years or more.”
He added that there was little risk of nuclear catastrophe despite the sites, which were already badly damaged in the 12-day war last year, recently being hit again. “It might have a very limited consequence, like chemical poisoning, but not nuclear as one might imagine,” he said.
Mr Grossi also warned it “cannot be excluded” that some factions in the Iranian government may be convinced by the continuing conflict that acquiring a nuclear weapon is necessary for Iran’s safety. “These are things that people think and I believe we need to avoid this scenario,” he said.
