Where does Iran get its uranium from?
Mainly from domestic sources. Iran has small proven uranium reserves, totalling about 3,000 tons. But surveys suggest it may have 10 times this amount. Iran almost certainly lacks enough uranium for civil nuclear power generation - but it does have sufficient amounts for a weapons programme.
Is Iran importing uranium from overseas?
There have been reports that Iran has sought uranium from the Democratic Republic of Congo, where export controls are non-existent. But nothing has ever been proved. Iran does have enough uranium of its own to build nuclear weapons.
Why is the West so concerned about Iran's nuclear facility at Natanz?
This is where enrichment of uranium is taking place. This process is critical because it could be used to produce weapons-grade uranium - the material essential to the manufacture of a nuclear bomb. That is why the United Nations has passed three resolutions calling on Iran to stop enriching uranium. The onset of enrichment on an industrial scale is a crucial act of defiance.
What is a centrifuge?
This is a machine used to separate the form of uranium used in nuclear fuel and bombs. In its natural form, uranium mostly comprises two isotopes - uranium-235 and uranium-238. Iran wants uranium-235 because it can undergo fission, the splitting of atoms to release energy. That energy can be used to generate electricity - or it can be unleashed in the force of a nuclear bomb.
How long might it take for Iran to produce enough weapons-grade uranium for one bomb?
Iran claims to have 3,000 centrifuges operating in Natanz. But experts say this is an exaggeration and it probably has about 1,000. If so, Iran would be able to make enough weapons grade uranium for one bomb in about two years, estimates David Albright, president of the Institute for Science and International Security in Washington. If Iran sets up 3,000 centrifuges, it might be able to produce the material for one bomb every year. But this is quite a challenge.
What is Iran's side of the story?
Teheran says that its nuclear programme is designed to generate electricity. Iran's population exceeds 70 million and the country's demand for power is enormous. It denies any ambition to produce a bomb.
Is Iran telling the truth?
Western governments disbelieve this explanation. Iran has the world's second largest reserves of oil and natural gas - so why does it need nuclear power to generate electricity? Apart from being uneconomic, this would also leave the country dependent on imported uranium. Moreover, Iran seems to be enriching more uranium than it could possibly use in the one power plant it has planned, at Bushehr. Lastly, UN inspectors in Iran have found unexplained traces of highly enriched uranium - which has no civilian use - in the country's nuclear plants.