The US under-secretary of state for political affairs said in Paris this evening that US policy was aimed at maintining UN Security Council unity on Iran.
A meeting of foreign ministers is scheduled for New York on 9 May.
Nicholas Burns said he expected a consensus to emerge over the next 30-40 days on the need to send a 'stiff message' to Iran.
He said a range of sanctions had been discussed privately.
Earlier, Iran threatened to attack Israel in response to any 'evil' act by the United States.
Tehran claimed it has enriched uranium to a level close to the maximum compatible with civilian use in power stations.
Last Friday, the UN's nuclear watchdog, the International Atomic Energy Authority (IAEA), said that Iran was violating a UN order to stop enriching uranium.
The US, Britain, France and Germany are pushing for a tough line to be taken against Tehran.
Russia and China are calling for a more cautious approach.
