The UN nuclear watchdog pressed Iran today to address suspicions about nuclear bomb research in the Islamic state, part of diplomatic efforts to resolve the dispute before any possible military action by Israel or the United States.
A flurry of bellicose rhetoric from some Israeli politicians this month has ignited speculation that Israel might strike nuclear sites before the US presidential election in November.
On the eve of today's talks between Iran and the United Nations' International Atomic Energy Agency (IAEA), diplomatic sources said that Iran had installed many more uranium enrichment centrifuges at its Fordow underground facility.
Though the new machines are not yet operating, the move signalled Tehran's defiance of international demands to suspend enrichment and may strengthen the Israeli belief that toughened sanctions are failing to make Tehran change course.
The sources also said satellite imagery indicated Iran had used a brightly coloured, possibly pink, tent-like structure to cover a building at a military site which the U.N. watchdog wants to inspect, raising new concerns about suspected cleansing of evidence of illicit past nuclear work there.
Iran, the Jewish state's arch-enemy and a major oil producer, denies it is seeking nuclear weapons and has threatened wide-ranging reprisals if attacked.
Iran's envoy to the IAEA, Ali Asghar Soltanieh, said he expected progress in Friday's meeting: "Both sides are trying to bridge the gap," he told reporters at Iran's mission in Vienna.
Chief UN inspector Herman Nackaerts, in charge of the agency's long-stalled inspection effort, said the aim was to reach an agreement on how to resolve the IAEA's questions about possible military dimensions to Iran's nuclear programme.
Mr Nackaerts, who headed the IAEA delegation, said he would reiterate his request for access to the Parchin military facility, where he believes Iran has undertaken explosives tests relevant for developing a nuclear weapons capability.
Their meeting is 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 nuclear enrichment programme, which is the immediate priority of the six powers - the United States, Britain, Russia, China, France and Germany. Refined uranium can have both civilian and military purposes.
Reuters