Iran also has a research reactor and had expressed interest in acquiring a heavy-water reactor and a gas centrifuge, which could be used to enrich fissile material. This centrifuge - which is clearly unnecessary for peaceful purposes - will not now be supplied by Russia, President Boris Yeltsin promised yesterday.
In January 1993, the Russian intelligence service acknowledged that Iran had a nuclear- weapons programme, but Moscow's position is far from clear- cut, as the Energy Ministry desperately needs money from nuclear sales, while the Foreign Ministry is concerned about the effect of this policy on relations with the United Nations and the West.
The proposed sale of the reactors would complete developments which began in 1974. Tehran ordered a number of nuclear reactors, under deals with the French and Germans.
Construction of the two German-based reactors at Bushehr began and one was about 80 per cent complete when the Shah was overthrown in 1979. Had the Shah survived, Iran would probably have nuclear weapons by now.
But the US now dislikes Iran and worries that Iranian nuclear plans make Israel less likely to accede to the nuclear Non-Proliferation Treaty (NPT). The question has also been asked why oil-rich Iran, with no energy shortage, needs to develop nuclear power.
The reactors the Russians propose to sell use low-enriched uranium, which is sealed in them for about three years. When most of it is "burnt", the residue includes isotopes of plutonium, which experts said yesterday were "not terribly suitable" for making nuclear weapons. The Iranians have said any spent plutonium will be returned to Russia; US diplomatic sources said there was no "significant risk of diverting plutonium".
The alternative route to a nuclear device would be to divert some of the low-enriched uranium, before it went into the reactors, and enrich it. The Russians have said they will put controls in place to ensure uranium is not diverted, and Iran has said it will accept more stringent safeguards than those specified under the NPT, extension of which is being debated in New York.
But last night US diplomatic sources said: "We're not reassured. We see a larger picture here. Iran's nuclear weapons programme is still fairly rudimentary. It's a long way behind Iraq's but it's hard to pin down. To wait for it to become visible would be to wait for too long, as we saw in the case of Iraq and North Korea."