"Iran's decision on enrichment, particularly research and development is irreversible," Iranian ambassador to the International Atomic Energy Agency (IAEA) Aliasghar Soltanieh said in Vienna.
Foreign Minister Manouchehr Mottaki, speaking in Geneva, described the UN declaration as an "angry precedent" and a "bad move".
Mr Mottaki, speaking to the UN Conference on Disarmament, said Iran would formally offer to set up a "regional consortium" to enrich fuel for its nuclear program, implying that it would be set up in Iran.
Iran struck the defiant stance even as foreign ministers of the Security Council permanent members plus Germany met in Berlin to chart their next moves in the stand-off.
Unanimous approval
The UN Security Council unanimously approved a non-binding statement giving Iran 30 days to abandon its uranium enrichment activities, ending a weeks-long impasse.
"This is a strong sign to Iran that negotiation not confrontation should be their course," US Secretary of State Condoleezza Rice said.
"It is now up to Iran to make a choice ... between isolation brought about by its own actions or a return to the negotiating table," said German Foreign Minister Frank-Walter Steinmeier, the meeting's host.
But cracks appeared between the major powers over how to act if Iran does not comply.
The UN statement leaves open what consequences might follow if Tehran does not halt uranium enrichment, and Russia and China insisted that economic sanctions or military action do not belong on the table.
"Russia does not believe that sanctions would serve the purpose of settling the various issues," said Russian Foreign Minister Sergei Lavrov.
In a clear warning against any the use of force to settle the standoff, Chinese Deputy Foreign Minister Dai Bingguo said that any such move would unleash chaos in the region.
"The Chinese side feels there has already been enough turmoil in the Middle East and we do not want to see more turmoil introduced into the region," he said.
The UN talks had been marred by differences between the United States and its Western allies on the one hand, and Russia and China on the other.
They’re at odds over how to coax Tehran away from uranium enrichment which could be used to build a nuclear bomb.
Watered down version
The statement that finally prevailed is a watered-down version of a Franco-British statement that calls on Iran to meet demands from the UN nuclear watchdog, the IAEA.
It expresses clear concern that Iran is trying to acquire nuclear weapons secretly, demands that Iran comply with the wishes of the IAEA governing board and calls for an IAEA report within 30 days.
The non-binding UN Security Council declaration was seen as a bid to placate Russia and China, which have opposed any hint of punitive measures against Iran, an ally and key trading partner.
In a further concession, the co-sponsors extended the deadline to 30 days from the 14 days they had initially sought.
The working lunch in Berlin also brought together Foreign Secretary Jack Straw of Britain, Foreign Minister Philippe Douste-Blazy of France and EU foreign policy chief Javier Solana.
Washington and European powers believe Iran has ambitions of building a nuclear bomb, which they argue would destabilise the entire region.
Tehran denies the charge and says its nuclear program is peaceful.