By Jonathan Marcus
BBC Diplomatic correspondent
A little over a month ago, Iranian President Mahmoud Ahmadinejad proudly announced that Iran had joined, as he put it, those countries which have nuclear technology.
He was speaking in the wake of a series of successful experiments in which Iranian scientists had taken uranium hexafluoride gas, introduced it into a small number of centrifuges, and produced a small quantity of low enriched uranium.
The message was simple. Iran's enrichment programme was under way and there would be no going back.
But Iran's technical capabilities may not be quite as advanced as they would have the world believe.
Western diplomatic sources have told the BBC that there is a very strong probability that the uranium hexafluoride gas used in these experiments was not made by the Iranians at all.
Iran says its nuclear programme is peaceful
They say that it may well have come from a small stock of material sold to Iran by China back in 1991.
This sale took place just before China itself joined the Non-Proliferation Treaty regime; hence before it was bound by the strict export controls that the treaty demands.
Indeed, diplomats say that it was China's decision to inform the International Atomic Energy Agency of this sale a few years later, that helped to start the process of unravelling what the Iranians were really up to.
Nuclear experts say that, in many ways, it is not surprising that Iran should use the Chinese material in its initial experiments.
Iran is widely believed to have had some problems with impurities in its own production of uranium hexafluoride gas.
Hence it would be logical to use the good quality Chinese material to test out its enrichment machinery.
Whether or not the experiments also used Iranian-manufactured feed-material is unknown.
The Iranian move clearly had great propaganda value.
Iranian President Mahmoud Ahmadinejad is clearly proud of the Iranian scientists' achievements.
But there may also have been a clear political purpose: to demonstrate that the Iranian enrichment programme is now a reality and to put down a marker that in the event of any future deal, Iran's right to conduct at least some enrichment activity will have to be acknowledged.
Think tanks and policy experts have produced a variety of plans to resolve the nuclear row with Iran.
Increasingly these do tend to allow the Iranians the right to limited enrichment activities: bowing, if you like, to the "fact" that Iran has seemingly already mastered the necessary technology.
The uncertainty surrounding Iran's technical progress underscores the broader questions about its overall nuclear ambitions.
Iran, of course, strenuously denies having any desire to develop a nuclear bomb.
But opinion differs as to how long it might take the Iranians to develop a "break-out" capability: that is to have a sufficiently capable civil enrichment capacity to allow them to renounce their treaty obligations and to push at full speed for a bomb.
And the uncertainty also highlights another fact, admitted by Western officials at least in private - that their hard intelligence on Iran's nuclear programme is as limited as their knowledge of Iraq's nuclear activities prior to the 2003 US-led invasion.