Britain and France, backed by the US, introduced a UN Security Council resolution on Wednesday demanding Iran suspend uranium enrichment that the West suspects is part of a secret nuclear weapons program.
The text, which is bound to be modified, does not call for sanctions but is tougher than expected. It threatens to consider "further measures as may be necessary," a veiled warning of sanctions that the West wants if Iran does defies council demands.
"This process is reversible if Iran complies," Britain's UN Ambassador Emyr Jones Parry said. "The problem is Iran is not complying."
The draft calls on all nations to "exercise vigilance" in preventing the transfer of materials and technology "that could contribute to Iran's enrichment-related and reprocessing activities and missile programs."
But Jones Parry said this provision was not a binding demand. Russia is the only major power still engaging in lucrative nuclear cooperation with Iran.
Russia, which along with China has opposed sanctions, was conciliatory about the draft. Its new UN ambassador, Vitaly Churkin, said he still had problems with the text but hoped a resolution could be adopted soon, before six foreign ministers meet on Monday and Tuesday in New York.
"Hopefully, we all like to do the hard work ourselves and leave the big things for our ministers," Churkin told reporters when asked about a council vote.
The resolution is under Chapter 7 of the UN Charter, which makes it mandatory under international law. It gives Iran another chance to comply prior to a deadline that has not yet been decided but diplomats hoped it would be in early June.
A Chapter 7 resolution allows sanctions or even war to enforce compliance but a separate resolution is required to specify either step.
Churkin would not answer when asked if Moscow would allow a Chapter 7 resolution if other parts of the text were modified.
But France's UN ambassador, Jean-Marc de la Sabliere, said, "We are used to negotiations and we know it is probably possible."
US Ambassador John Bolton told reporters, "The fundamental point is for Russia and China to agree that this is a threat to international peace and security under Chapter 7."
"If they are prepared to accept that, which I see as central to the resolution, we will see what else is possible," he said.
"It will be clear from the way the resolution is worded that we will call Iran to suspend enrichment," Bolton told reporters before joining the 15-nation council for a closed-door meeting.
Russia and China, which could kill any resolution by using their veto power, are reluctant to endorse anything that might be seen as a step toward possible later sanctions or military action, although this draft does not threaten either measure.
However, the Western allies want targeted sanctions if Iran defies this resolution, including a restrictions on a transfer of nuclear technology as well as a travel ban on individuals.
One key provision in the resolution states that "Iran shall suspend all enrichment-related and reprocessing activities, including research and development" and "suspend the construction of a reactor moderated by heavy water."
Since 2004, Iran has been building a heavy water reactor at Arak, 193km southwest of Tehran, which experts say raises concerns because it could produce bomb-grade plutonium.