Western powers believe that Iran is running short of the raw material required to manufacture nuclear weapons, triggering an international race to prevent it from importing more, The Times has learnt.

Diplomatic sources believe that Iran’s stockpile of yellow cake uranium, produced from uranium ore, is close to running out and could be exhausted within months. Countries including Britain, the US, France and Germany have started intensive diplomatic efforts to dissuade major uranium producers from selling to Iran.

Before Christmas, the Foreign and Commonwealth Office sent out a confidential request for its diplomats in Kazakhstan, Uzbekistan and Brazil, all major uranium producers, to lobby governments not to sell uranium products, specifically yellow cake, to Iran.

Iran’s stock of yellow cake, acquired from South Africa in the 1970s under the Shah’s original civil nuclear power programme, has almost run out. Iran is developing its own uranium mines, but does not have enough ore to support a sustained nuclear programme.

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It was shortly before Christmas that diplomats at Britain’s sleek new embassy on Kosmonavtov Street in the Kazakh capital of Astana received a confidential and urgent request. Iran, officials back in Whitehall advised, was believed to be close to running out of its stockpiles of yellow cake — a powdered form of uranium ore.

There were concerns that Tehran could be seeking fresh supplies to support its nuclear programme at a critical juncture — just months before intelligence experts expected it to have accumulated enough enriched material for a bomb. British officials were to urge Kazakhstan, one of the world’s biggest producers, to ignore any possible approaches to obtain imports.

The request, news of which emerged after an international investigation by The Times, was part of a drive by six countries — Britain, the US, France, Germany, Australia and Canada — to choke off supplies of uranium to Iran. It is a move that, while unlikely to cripple any effort to develop a bomb, would blunt its ambitions and help to contain the threat, authoritative sources said.

Kazakhstan, with 15 per cent of the world’s deposits, is an increasingly important player in the global uranium trade and has set a target this year to become the world’s largest producer.

Uzbekistan, where British officials are involved in a similar lobbying exercise, also has large deposits and was a leading supplier for weapons-grade material during Soviet times.

While there is no direct evidence that Iran has actively sought to buy uranium from either country, Western intelligence sources view them as one of a number of potential weak spots in the supply chain.

Others include the Democratic Republic of Congo (DRC), where uranium for the bombs dropped on Japan in 1945 was mined and where there have been persistent rumours of illegal exports to countries including Iran. Getting to the truth about such claims is notoriously difficult. Reports by British Intelligence of an attempt by Saddam Hussein to acquire substantial quantities of yellow cake from Niger in West Africa for a clandestine nuclear bomb project turned out to be fabricated. That did not stop President Bush referring to them, in March 2003, as part of the justification for the invasion of Iraq.

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