A claim by President Ahmadinejad that Iran has 3,000 working uranium-enriching centrifuges sent a tremor across the world yesterday amid fears that Israel would respond by bombing the countrys nuclear facilities.

Military sources in Washington said that the existence of such a large number could be a tipping point, triggering an Israeli air strike. The Pentagon is reluctant to take military action against Iran, but officials say that Israel is a different matter. Amid the international uproar, British MPs who were to have toured the nuclear facility were backing out of their Iran trip.

Even before President Ahmadinejads announcement, a US defence official told The Times yesterday: Israel could do something when they get to around 3,000 working centrifuges. The Pentagon is minded to wait a little longer. US experts say 3,000 machines running for long periods could make enough enriched uranium for an atomic bomb within a year.

Israel responded by serving notice that it would not tolerate a nuclear Iran. Talks never did, and never will, stop rockets, said Ehud Barak, the Defence Minister, after talks with the security cabinet. Concern about Israels intentions has been heightened by its recent air strike on a suspected nuclear plant in Syria. In 1981 Israel destroyed Saddam Husseins Iraqi nuclear reactor, and as the sole if undeclared nuclear power in the region, it now considers Iran the most serious threat to its security.

Efraim Inbar, of the Begin-Sadat Centre for Strategic Studies in Tel Aviv, said that the figure of 3,000 centrifuges would signal the ability of Israels arch-foe to produce the nuclear material needed for a warhead. I wouldnt be surprised if we do something if the international community leaves us alone, he said. I think we [Israel] are preparing for it. For Israel this is a critical technological moment.

Tehran says it plans to expand its enrichment programme to up to 54,000 centrifuges at Natanz in central Iran, which would amount to industrial-scale uranium enrichment.

Mr Ahmadinejad, speaking yesterday at a rally, said that UN sanctions had failed to halt uranium enrichment. The world must know that this nation will not give up one iota of its nuclear rights . . . if they think they can get concessions from this nation, they are badly mistaken, he said. He has in the past claimed that Iran succeeded in installing the 3,000 centrifuges at its uranium enrichment facility but yesterdays speech was the first time he had said all of them were now operational.

The International Atomic Energy Authority recently put the figure at closer to 2,000, with another 650 being tested. The IAEA said yesterday: We will be publishing a report next week. We will not make any comment about this until then. Javier Solana, the EU foreign policy chief, is shortly to report on Irans willingness to give up uranium enrichment in exchange for political and trade incentives.

But the Israelis have recently expressed distrust of the IAEA. BBC reports today that a senior Israeli minister, Deputy PM Shaul Mofaz, has called for the sacking of IAEA head Mohamed ElBaradei. Mofaz said the Egyptian head of the International Atomic Energy Agency had endangered world peace by neglecting Iran's nuclear programme.

Mr. ElBaradei has said Iran's nuclear programme is not an immediate threat and if it wanted to build a nuclear bomb it would need years to do so. The IAEA report next week will help determine whether the United Nations imposes a third set of sanctions on Tehran.

"The policies followed by ElBaradei endanger world peace. His irresponsible attitude of sticking his head in the sand over Iran's nuclear programme should lead to his impeachment," Mr Mofaz said during a visit to Washington.