A defiant Iran shrugged off Wednesday the threat of new sanctions as Brazil and Turkey urged the United Nations to wait and see how a nuclear swap deal plays out before caving in to US pressure.

US President Barack Obama said he was "pleased" by developments after usual standouts Russia and China gave their backing to a tough new draft sanctions resolution circulated Tuesday to the full UN Security Council.

"We agreed on the need for Iran to uphold its international obligations or face increased sanctions and pressure, including UN sanctions," Obama said after talks with visiting Mexican counterpart Felipe Calderon.

"And I'm pleased that we've reached an agreement with our P5 plus-1 partners on a strong resolution that we now have shared with our Security Council partners."

But Security Council members Turkey and Brazil urged the world body not to impose new sanctions until Iran had been given time to honour a deal they brokered to swap about half its low enriched uranium (LEU) for nuclear fuel.

"Brazil and Turkey are convinced that it is time to give a chance for negotiations and to avoid measures that are detrimental to a peaceful solution," read a letter signed by their foreign ministers.

The two countries forged a deal Monday they hailed as a step toward ending Iran's years-old standoff with the West, but which US Secretary of State Hillary Clinton framed as an attempt by Tehran to avoid further punishment.

Under the deal, the Islamic republic agreed to ship out much of its stockpile of low enriched uranium to neighbouring Turkey in exchange for fuel for a research reactor for medical isotopes.

"This agreement is a new fact that has to be evaluated," Brazilian Foreign Minister Celso Amorim, who led the Iran-Brazil-Turkey negotiations, insisted in Brasilia.

Iran, which maintains that its nuclear enrichment activities are purely for civilian energy purposes and not aimed at building an atomic weapon as the West fears, suggested that the international desire for new sanctions was wilting.

"(Talk of) imposing sanctions has faded and this resolution is the last effort by the West," the Fars news agency quoted Vice President Ali Akbar Salehi, who also heads Iran's atomic energy organisation, as saying.

The new draft being considered by the Security Council foresees cargo ship inspections and new banking controls.

It would also expand an arms embargo and measures against Iran's banking sector as well as ban sensitive overseas activities like uranium mining and developing ballistic missiles.

The draft has the blessing of all five veto-wielding permanent members of the Security Council, plus Germany -- a significant boon to the US after months spent trying to persuade Moscow and particularly Beijing to come on board.

China's backing of a fourth round of sanctions against Iran came despite its earlier support for the fuel swap deal.

"We attach importance to and support this agreement," Chinese foreign ministry spokesman Ma Zhaoxu said after Monday's accord was struck.

Given the Brazil-Turkey letter, China's apparent reluctance to comment on new sanctions and Russia speaking only of its "understanding in principle... on the draft resolution," Salehi expressed doubts there was an emerging international consensus against his country.

"We should be patient because they won't prevail and by pursuing the passing of a new resolution they are discrediting themselves in public opinion," he said.

"I think there are some rational people among them who will stop them from making this irrational move."

Iranian Foreign Minister Manouchehr Mottaki expressed similar scepticism about the chances of new sanctions being passed.

"There is no chance the resolution is going to be passed," he told state-run Al-Alam television from the Tajik capital Dushanbe. "The nations who are seeking to impose sanctions are in the minority."

Already under three sets of UN sanctions over its defiance of repeated ultimatums to suspend uranium enrichment, Iran touted its agreement with Brazil and Turkey as a goodwill gesture that paves the way for a resumption of talks with the major powers.

The deal is similar to one suggested last year by the P5 plus 1, who had been negotiating with Iran over its nuclear programme until their patience ran out at the end of last year.

The US says its main objection to the new deal is that there is no commitment from Iran to suspend its enrichment activities.

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