The UN nuclear watchdog and Iran failed yesterday to strike a deal aimed at allaying concerns about suspected nuclear weapons research by Tehran, a setback in diplomatic efforts to resolve the standoff before any Israeli or US military action.

A flurry of bellicose rhetoric from some Israeli politicians this month has fanned speculation that Israel might hit Iran’s nuclear sites before the US presidential election in November.

Tensions went up another notch on the eve of yesterday’s talks between Iran and the International Atomic Energy Agency (IAEA) when diplomatic sources said Iran had installed many more uranium enrichment centrifuges at its Fordow underground site.

While the new machines are not yet operating, the move reaffirmed Iranian defiance of international demands on it to suspend enrichment and may strengthen the Israeli belief that toughened sanctions and concerted diplomacy are failing to make the Islamic Republic change course.

“The discussions today were intensive but important differences remain between Iran and the UN that prevented agreement,” Herman Nackaerts, the International Atomic Energy Agency’s chief inspector, told journalists after about seven hours of talks with an Iranian delegation in Vienna.

“At the moment we have no plans for another meeting.”

Little headway appeared to have been made on the IAEA’s most urgent request - access to the Parchin military facility, where the IAEA believes Iran has undertaken explosives tests relevant for developing a nuclear weapons capability.

Iran’s ambassador to the Vienna-based IAEA, Ali Asghar Soltanieh, said that “undoubtedly some progress” was made but that differences remained.

“Because it is a very complex issue ... issues related to national security of a member state are something very delicate,” the veteran Iranian diplomat said.

“But I have to say that we are moving forward ... and we are going to continue this process so that we at the end of the day will have a framework agreed by both sides.” Soltanieh had said before the talks began: “Both sides are trying to bridge the gap.”

The diplomatic sources who revealed the expansion of centrifuge capacity at Fordow also said satellite imagery indicated Iran had used a brightly coloured tent-like structure to cover a building at Parchin, increasing concern about possible cleansing of evidence of illicit past nuclear work there.

Israel signalled its patience with diplomacy was fading.

“Only yesterday we received additional proof that Iran is continuing accelerated progress towards achieving nuclear weapons and is totally ignoring international demands,” Israeli Prime Minister Benjamin Netanyahu said yesterday before the talks ended.

Asked about the outcome, a Western diplomat accredited to the IAEA told Reuters: “As dismal as expected.”

Iran denies it is seeking nuclear weapons and has threatened wide-ranging reprisals if attacked.

Nackaerts, the IAEA’s global chief of inspections, said before the meeting that the broader objective was an accord on how to resolve the UN watchdog’s questions about possible military dimensions to Iran’s nuclear programme.

It was the first meeting between the two sides since discussions in early June petered out in failure, dashing previous hopes that an accord might be near.

The talks were separate from Tehran’s negotiations with world powers that
have made little headway since they resumed in April after a 15-month hiatus, but the focus on suspicions about Iran’s nuclear ambitions mean they are still closely linked.

Washington says there is still time for diplomatic pressure to work in making Iran curb its enrichment programme, which is the immediate priority of the six powers - the US, Britain, Russia, China, France and Germany.

Refined uranium can fuel nuclear power plants or nuclear bombs, depending on the level of enrichment.

Iran says it seeks only civilian nuclear energy.

But its refusal to limit and open up its atomic activity to unfettered IAEA inspections that could determine whether it is purely peaceful, or not, has led to harsher punitive sanctions and louder talk about possible military action.