Doubts Over Iran Nuclear Capacity
Doubts have been raised about how technically advanced Iran's nuclear programme is, after it emerged Tehran may have used material from China. Western diplomatic sources told the BBC the feedstock for Iran's recent uranium enrichment experiments probably came from materials supplied in 1991.
That was before China joined the Non-Proliferation Treaty, and before it was bound by its export controls. READ MORE
Iran recently announced it had enriched uranium in its possession.
This was despite calls from Western powers to suspend the programme because of fears it could lead to the production of a nuclear weapon.
Nuclear experts say Iran has had some problems with impurities in its own production of the feedstock - uranium hexafluoride gas.
Iran used stocks of high-quality uranium gas from China to speed up a breakthrough in enrichment, diplomats say.
The Iranian move had great propaganda value, but it may also have had a clear political purpose; to demonstrate that the Iranian enrichment programme was a reality, says the BBC's Jonathan Marcus.
It may also have put down a marker that in the event of any future deal, Iran's right to conduct at least some enrichment activity would have to be acknowledged, our correspondent says.