President Bush said today that the threat of a nuclear-armed Iran was unnacceptable and posed a "grave threat" to global security.

Appearing at a White House press conference following talks with Angela Merkel, on her first visit to Washington as German Chancellor, the President condemned what he said were Tehran's clandestine attempts to gain nuclear expertise through the guise of a civilian programme.

"The development of know-how and or nuclear weapons is unnacceptable because an Iran armed with a nuclear weapon poses a grave threat to the security of the world," President Bush said.

"Countries such as ours have a great responsibility to work together and send a common message to Iran that it's behaviour... trying to clandestinely develop a nuclear weapon or using the guise of a civilian programme to get the know-how ... is unacceptable," he said.

The President recalled the statements made by President Ahmadinejad, Iran's hardline new ruler, in which he called for Israel to be "wiped off the map".

"And that’s unacceptable. And the development of a nuclear weapon seems to me would make them a step closer to achieving that objective," he said.

Mr Bush said he did not want to prejudge what action the United Nations Security Council might take against Iran, but added that referring Iran to the UN was part of a message to Tehran. "It’s logical that a country which has rejected diplomatic efforts to end the nuclear crisis be sent to the United Nations Security Council."

Mr Bush spoke after Iran threatened to end its co-operation with the UN atomic watchdog if its nuclear programme was referred for possible sanctions.

The move would stop the snap inspection of Iranian nuclear facilities and could bring an end to a moratorium on its enrichment of uranium. It would also jeopardise diplomatic negotiations with Britain, France and Germany, the three European powers who have been leading international efforts to prevent Iran developing nuclear weapon technology.

"If the dossier is sent to the Security Council, the European countries will lose the means which are currently at their disposal, because... the government will be obliged, in conformity with the law adopted by parliament, to end all its voluntary measures of cooperation," Manouchehr Mottaki, the Iranian Foreign Minister, told the IRNA news agency today.

Iran’s stand-off with the international community escalated on Tuesday when Tehran, which says it is simply trying to develop a nuclear power industry, broke International Atomic Energy Agency (IAEA) seals at its underground nuclear facility at Narantz in central Iran.

The Narantz plant is used for uranium enrichment, a necessary process to produce nuclear fuel but which can also be used to produce the material for bombs.

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