She said that Tehran should take the opportunity offered by EU diplomatic efforts, which Rice said Washington was watching closely for signs of progress.

"We've set no deadline, no timeline," she said, when asked how long the US administration would let those talks continue before pushing for other action. "The Iranians know what they need to do."

"The Iranians have to be held to their international obligations. We haven't set any timetables. We continue to be completely in close consultation with the Europeans, about how it is going, about whether progress is being made."

The United States suspects the Islamic Republic of seeking to develop nuclear weapons, and wants to take the case to the UN Security Council. The Europeans have favoured seeking to resolve the issue through negotiations.

Rice reiterated that Tehran should "take the opportunity" provided by the Europeans to find a negotiated solution to the standoff.

"I believe that everybody is telling the Iranians that they are going to have to live up to their international obligations or next steps are in the offing," she said, adding: "Everybody understands what next steps means."

"It is obvious that if Iran cannot be brought to live up to its international obligations that in fact the IAEA statutes would suggest that Iran has to be referred to the UN Security Council," she said.

"The Iranians should take the opportunity that the Europeans are giving them to live up to their obligations," she added.

"The message is there. The Iranians need to get that message. We can certainly always remind them that there are other steps that the international community has at its disposal should they not be prepared to live up to those obligations."

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