Britain and Germany have warned Iran it could be hauled before the UN Security Council over its nuclear ambitions, but both countries said they still hoped for a diplomatic way out of the impasse.
Since Iran's 18-year secret nuclear programme was exposed three years ago, European Union nations Britain, France and Germany have tried to find a way to ensure Iran cannot make an atomic bomb while developing civilian nuclear technology.
Their patience has worn thin after three years of talks and the "EU3" has backed American calls, endorsed unanimously by the US Senate on Friday, for Iran to be reported to the Security Council for a vote on economic sanctions.
Foreign ministers of the five permanent Security Council members, plus Germany, meet in London on Monday to see if they can agree to call for Iran to be referred to the UN at an emergency meeting of the International Atomic Energy Agency (IAEA) in Vienna on Thursday.
"We are trying to persuade Iran to come back into compliance. There is some intense diplomacy taking place over this weekend," Foreign Secretary Jack Straw told Reuters on the sidelines of an economic summit in Davos, Switzerland.
"We will make judgements in the light of discussions which will occur on Monday in London," he said on Saturday.
Signs of reluctance from veto-wielding Security Council members Russia and China to go down the sanctions route are likely to undermine the U.S. and European calls.
But Germany's Foreign Minister said sanctions against Iran were still possible.
"To rule out economic sanctions would be unwise," Frank-Walter Steinmeier said in an interview with German weekly magazine Der Spiegel. But hopes of a diplomatic solution were "by no means exhausted", he said.
Iran insists it only wants nuclear power to generate electricity to satisfy booming domestic demand.
But suspicions surround Tehran's nuclear activities, partly resumed this month when Iran removed UN seals and resumed sensitive atomic fuel research.
Iran has countered U.S. efforts to send it to the Security Council with a mixture of threats and concessions.
Tehran's foreign minister said on Saturday his country would cease co-operation with UN nuclear inspectors if the IAEA referred Iran to the UN Security Council.
"Any possible action by the board of governors (of the IAEA) in informing the UN security council about Iran's nuclear project in their February meeting, as I said before, will trigger the government to cut all its voluntary measures as per the law," Manouchehr Mottaki told a news conference.
But Iran has also pledged to let UN inspectors examine equipment from the former Lavisan military site, a senior diplomat said on Friday. The move appeared to be aimed at averting an IAEA vote for UN referral, he said.
Iran tore down a military-linked physics research centre at Lavisan in 2004 and stripped the ground around it before IAEA investigators could test for particles on equipment they believed was obtained by Iran for use in enriching uranium.
"The latest signals from Tehran are contradictory at best," Steinmeier said in an advance copy of an interview due out in Der Spiegel's Monday edition.
"I'm aware of the criticisms that Iran is using tricks and playing for time -- and I can't seriously deny them," he said.
Russia and China oppose the Western thrust to refer Tehran to the Security Council, calling it premature, and the EU has been amending a resolution for the February 2 IAEA meeting in search of consensus with key non-Western member states, diplomats say.
An EU diplomat said the text was being tweaked to help meet Moscow's demand that the IAEA only "inform" the Council about Iran and leave a referral motion until the March IAEA meeting.
Mottaki said Tehran and Moscow had agreed for more countries to participate in a plan to enrich uranium for Iran in Russia, but he did not elaborate.
Conducting the nuclear fuel work in Russia would convince Washington and the EU that the uranium could not be used to make atomic weapons, but Tehran has blown hot and cold on the idea.
Mottaki said more work was needed on the plan.
"If some factors are added to that plan to make it an integrated one, it could become a new approach in continuing Iran's nuclear issue," he said.