Iran gained the technicaly capability to produce highly enriched uranium in sufficient quantities to make nuclear weapons in March 2009, according to US officals.
The leaked diplomatic cables, published by WikiLeaks, published a memorandum of a Vienna meeting in which the US representative said the Iranian nuclear facility in Natanz was capable of enriching uranium stocks into uranium hexafluoride gas in sufficient quantities to make nuclear bombs.
The assessment came just weeks after the International Atomic Energy Agency had concluded that Iran had enriched just over one tonne of uranium to a threshhold level of enrichment and needed just half a tonne more to be ready to manufacture an initial warhead.
It said: "Iran had now demonstrated centrifuge operations such that it had the technical ability to produce highly enriched uranium (HEU) if it so chose".
The remarks were made at a meeting hosted by Simon Smith, the British ambassador, at which diplomats discussed a containment strategy to slow down Iran's progress to nuclear capacity.
British officials were reported to have predicted that Iran's scientists would have accumulated 20 tonnes of the material, enough for more than a dozen weapons by 2014.
Since the meeting, Iran's nuclear programme has suffered significant setbacks after computer networks at its facilities were infected by the Stuxnet virus. The virus targets the operating system of sophisticated rotors, varying the speed of the devices thus making them unstable and ultimately unless.
Experts have estimated that more than half of Iran's enrichment centrifuges have since been sabotaged or fallen into disrepair.
The US report matched the assessment given by Denis Blair, the US intelligence chief, at a Congressional session in the same month.
At the same meeting France warned that Iran could attempt to obtain uranium yellowcake, the raw material for nuclear fuel and weapons, from Congo.
The cables also revealed worldwide efforts to cut off Iran's access to highly engineered steel and carbon fibre products needed to manufacture more sophisticated centrifuges.