Rice said seeking UN action against Tehran was a "reasonable option" after the Iranians resumed last month sensitive fuel-cycle work they had suspended in November as part of negotiations with Britain, France and Germany.

"Iran needs to get a message from the international community that is a unified message, and by this I mean not just the EU-3 and the United States, but also Russia and China and India and others," Rice said.

Washington has long been lobbying for a consensus within the International Atomic Energy Agency (IAEA), the UN watchdog, to take steps against Iran which insists its nuclear program is strictly peaceful.

The EU-3, which has been trying to persuade the Iranians to renounce any nuclear ambitions in return for a package of economic and security incentives, appeared Friday to have run out of patience.

A confidential document obtained by AFP, containing notes for IAEA diplomats, said the EU was ready to call for Iran to be brought before the UN Security Council as a "clear signal of concern" over its activities.

The IAEA board is due to meet on September 19 to discuss a new report issued last week by the agency's director Mohamed ElBaradei, who said Iran had failed to completely allay suspicions over its nuclear intentions.

"We've all said that a next step to be expected would be referral to the Security Council," Rice said Friday.

"I think that after the IAEA report of a couple of days ago it's clear that Iran is not living up to its obligations and so UN Security Council (referral) seems to be a reasonable option."

But India, China and Russia have balked at bringing in the United Nations. The State Department said Thursday it had lodged a protest, specifically with New Delhi.

Under Secretary of State for Political Affairs Nicholas Burns told Congress Rice would also raise the issue with her Indian counterpart Natwar Singh and Prime Minister Manmohan Singh during talks outside a UN Summit next week.

Rice said Friday, "It is not acceptable for Iran to enter into negotiations that are aimed at restoring confidence that they are going to live up to their international obligations and then summarily walk out on them."

She expressed confidence the US and EU call for UN action would prevail.

"I think the question has been answered by a number of people, including Europeans, who said that if the Iranians will not come back to the negotiations ... then not many choices are going to be left to the international community but the Security Council."

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