The world’s leading powers today joined in a chorus of condemnation of Iran for advancing its atomic programme in defiance of the United Nations.

Mahmoud Ahmadinejad, the Iranian President, declared yesterday that Iran had produced its first batch of enriched uranium and would now press ahead with industrial-scale enrichment.

His announcement kept Tehran on a collision course with the United Nations Security Council, which last month ordered it to halt all work on nuclear enrichment. Many Western countries fear that Iran is pursuing atomic weapons, not just fuel for power stations as it insists.

Condoleezza Rice, the US Secretary of State, said today that the UN Security Council would need to meet again on the issue, and take "strong steps to make certain (to) maintain the credibility of the international community".

She did not say what those steps might be, but her spokesman, Sean McCormack, said they would be stronger than the presidential statement already issued by the Security Council.

Scott McClellan, the main White House spokesman, said that sanctions against Iran remained "a possibility as well, one option that’s available".

Russia and China - traditionally sympathetic to Tehran - added their voices to the chorus of criticism. Both are important players on the Iran issue, with veto rights at the Security Council, and have hitherto opposed sanctions against a country that is one of their major trading partners. Today Sergei Lavrov, the Russian Foreign Minister, urged Iran to stop all enrichment work but repeated that the use of force could not solve the stand-off over Iran’s nuclear programme.

"If such plans exist they will not be able to solve this problem. On the contrary they could create a dangerous explosive blaze in the Middle East, where there are already enough blazes," he said.

George Bush, the US President, this week dismissed media reports of plans for strikes on Iran as "wild speculation" and saidthat force might not be needed to curb its nuclear ambitions.

Wang Guangya, China’s UN Ambassador, said that Tehran’s enrichment move was"not in line with what is required of them by the international community".

But a senior Iranian official ruled out any retreat. "Iran’s nuclear activities are like a waterfall which has begun to flow. It cannot be stopped," said the official, who asked not to be named.

Mohamed ElBaradei, the head of the International Atomic Energy Agency (IAEA), will visit Iran tomorrow to seek full Iranian cooperation. The IAEA, whose inspectors are in Iran investigating nuclear sites, has given no comment on Iran’s statements. But an agency diplomat said:"The timing was strange but it may have been intended by them to improve their bargaining position."

Kofi Annan, the UN Secretary General, urged all parties to return to talks to defuse the crisis. "I appeal to everyone to actively work to search for a diplomatic solution and to cool down the rhetoric and not to escalate," Mr Annan told Reuters after a meeting with Jan Peter Balkenende, the Dutch Prime Minister, in The Hague.

Britain, France and Germany, who brokered a deal to suspend enrichment which broke down last year, weighed in with criticism of Iran.

Jack Straw, the British Foreign Minister, said that the announcement was "deeply unhelpful" and undermined confidence. His German counterpart, Frank-Walter Steinmeier, said that Iran was"going in precisely the wrong direction" for a return to negotiations.

Philippe Douste-Blazy, that French Foreign Minister, said that it was a worrying step and Iran should stop its"dangerous activities".

The US State Department said that it was unable to confirm that Iran had enriched uranium and some experts said even if Tehran’s assertions were accurate, it would still be years before the Islamic Republic was able to produce a nuclear weapon.

The level of enrichment needed for nuclear bombs is far higher than the 3.5 per cent that Iran says that it has reached.

It would take Iran about two decades to yield enough highly enriched uranium for one bomb with its current cascade of 164 centrifuges. But Tehran says it wants to install 3,000 centrifuges, enough to produce material for a warhead in a year.

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