http://www.ft.com/cms/s/0/f367aada-fec8-11dd-b19a-000077b07658.html
By Daniel Dombey

Iran has now built up a stockpile of enough enriched uranium for one nuclear bomb, United Nations officials acknowledged on Thursday.

In a development that comes as the Obama administration is drawing up its policy on negotiations with Tehran over its nuclear programme, UN officials said Iran had produced more nuclear material than previously thought.

They said Iran had now accumulated more than one tonne of low enriched uranium hexafluoride at a facility in Natanz. If such a quantity were further enriched it could produce more than 20kg of fissile material – enough for a bomb.

“It appears that Iran has walked right up to the threshold of having enough low enriched uranium to provide enough raw material for a single bomb,” said Peter Zimmerman, a former chief scientist of the US Arms Control and Disarmament Agency

The new figures come in a report by the International Atomic Energy Agency, the UN’s nuclear watchdog, released on Thursday.

This revealed that Iran’s production of low enriched uranium had previously been underestimated.

When the agency carried out an annual stocktaking of Natanz in mid-November Iran had produced 839 kg of low enriched uranium hexafluoride – more than 200kg more than previously thought.

Tehran then produced an additional 171 kg by the end of January.

“It’s sure as hell certain that if they didn’t have it [enough] when the IAEA took these measurements, they will have it in a matter of weeks,” Mr Zimmerman said.

Iran’s success in reaching such a “breakout capacity” – a stage which would allow it to produce enough fissile material for a bomb in a matter of months – crosses a “red line” that for years Israel has said it would not accept.

However, UN officials emphasise that in order to produce fissile material Iran would have to reconfigure its Natanz plant to produce high enriched uranium rather than low enriched uranium – a highly visible step that would take months – or to shift its stockpile to another clandestine site.

No such sites have been proved to exist, although for decades Iran hid evidence of its nuclear programme.

A senior UN official added that countries usually waited until they had an enriched uranium stockpile sufficient for several bombs before proceeding to develop fissile material. But he conceded that Iran now had enough enriched uranium for one bomb.

“Do they have enough low enriched uranium to produce a significant quantity [enough high enriched uranium for a bomb]?” he asked. “In theory this is possible, [although] with the present configuration at Natanz it isn’t.”

David Albright, the head of the Institute for Science and International Security, said: “”If Iran did decide to build nuclear weapons, it’s entering an era in which it could do so quickly.”