The United States, Britain and France introduced a UN Security Council resolution this evening demanding Iran suspend its uranium enrichment programme.
The resolution does not threaten any punitive action but still faces opposition from Russia and China.
The text calls for consideration of "further measures as may be necessary" to ensure Iran's compliance the resolution - indicating that sanctions should not be ruled out if Tehran remains defiant.
It also calls on nations to "exercise vigilance" in preventing the transfer of technology that could contribute to Iran's nuclear programmes.
The resolution is under Chapter 7 of the UN Charter, which makes it legally binding. It gives Iran another chance to comply with the council's demands prior to a deadline that has not yet been decided.
A Chapter 7 resolution allows sanctions or military action to enforce compliance but a separate resolution would be required to activate either step.
Russia and China, which could use their veto power if such measures were sought, are reluctant to endorse any move that might be seen as a step toward possible later sanctions or military action.
"This resolution will not deal with sanctions," US Ambassador John Bolton said, adding that it was not in Russia's interest "to be within the range of another nuclear power."
Britain's UN ambassador, Emyr Jones Parry said his country, France and Germany believed "the Security Council now needs to respond to indicate how it intends to proceed in the light of the absence of compliance by Iran."
The key paragraph in the resolution states: "Iran shall suspend all enrichment-related and reprocessing activities, including research and development" and "suspend the construction of a reactor moderated by heavy water."
The foreign ministers of Germany, the United States, Britain, France, Russia and China meet on the issue in New York on Monday and Tuesday but there is little chance the resolution would be adopted before then.
Iran maintains its nuclear programme is legal and peaceful and recently even accelerated uranium enrichment but is still far below the level needed to make an atomic bomb.