Existing demands: On March 17 the UN Security Council approved a statement, echoing earlier resolutions from the International Atomic Energy Agency (IAEA) calling for Iran to suspend its uranium enrichment programme and answer questions concerning its nuclear research.
Current action: UN diplomats from the US, Britain and France are due to begin drafting a resolution they hope to introduce to the Security Council within the week.
According to John Bolton, the American ambassador to the UN, it would force Iran legally to comply with the council's demands.
The resolution would be adopted under Chapter 7 of the UN Charter that makes council resolutions mandatory under international law. Chapter 7 allows for sanctions or even war but a separate resolution is required to specify either step.
Future action: If Tehran refuses to comply, the Western powers will attempt to impose targeted sanctions against individuals in Iran, Bolton said. If sanctions are impossible in the Security Council, the United States says it will try to pursue them with like-minded allies.
John Bolton is keen on strong
action concerning Iran
Opposition: Russia and China, which have Security Council veto power, fear that excessive pressure on Iran could be self-defeating or, worse, precipitate an oil crisis.
Both oppose sanctions and worry the US would use a tough council resolution as a means to justify military action.
Iranian attitude: Iran argues that three years of IAEA inspections have not discovered a weapons programme.
But its diplomats have revealed that Tehran has offered, in private talks with European representatives, to slow down nuclear programmes if the Security Council takes no action.
What next: No date has been set for a vote on the potential UN resolution, which often takes longer to negotiate than its backers predict.
Senior foreign ministry officials from the US, Britain, France, Russia, China and Germany meet in Paris on May 2 to discuss the Iran issue and foreign ministers from the same countries will meet at the United Nations on May 9.