The Bush administration has said it sees no sign that Iran will meet a UN deadline to curb its nuclear programme, and that the world body should quickly respond with international sanctions.
"If they do not meet the requirements of the UN Security Council resolution, then we would expect that the parties would immediately begin formal discussions about a resolution that would call for sanctions," State Department spokesman Sean McCormack said on Wednesday.
He spoke one day before the UN deadline for Iran to stop uranium enrichment.
"They've said that they don't intend to comply, and we'll see if they pull a rabbit out of the hat," "I don't think anybody expects that at the moment."
Diplomats from the permanent members of the UN Security Council, plus Iran negotiating partner Germany, will meet next week in Europe to begin work toward sanctions, McCormack said.
He described a graduated approach that could take weeks or months, with lesser penalties applied to Tehran as a first step.
He would not give a specific menu of possible penalties, but US and European diplomats have suggested that some new limits on Iranian exports and travel by its government officials could be approved with relative ease.
"We think that this first resolution should send a substantial signal to the Iranian regime that this is serious business and that the international community means what it says," McCormack said.