Western powers have said they will push for a legally binding UN resolution to force Iran to comply with calls for it to cease uranium enrichment.
Iran says its nuclear programme is for purely peaceful purposes
US ambassador John Bolton said there was a sense of urgency about the move.
On Friday the UN's nuclear watchdog said in a report that Tehran had ignored Security Council calls.
Iran said it was willing to find a constructive solution but would not respond to pressure from the international community.
The UN wants the research halted amid Western fears - denied by Iran - that Tehran might develop nuclear weapons.
The stage is set for months of diplomatic confrontation, the BBC news website's world affairs correspondent Paul Reynolds says.
US President George W Bush said the report showed Iran's intransigence and the United States would continue to consult its allies over what he termed Iran's nuclear weapons ambitions.
IRAN CRISIS: NEXT STEPS
2 May: Negotiators from US, Russia, China, UK, France and Germany meet in Paris
3 May: Possible Security Council meeting to discuss IAEA report
9 May: Foreign ministers from US, Russia, China, UK, France and Germany meet at UN
Mr Bolton said it was clear that Iran had accelerated its nuclear programme and that he hoped the Security Council would act as soon as possible.
"We do think there's a sense of urgency here and we hope that we can get council action just as soon as possible," he said.
But UK ambassador Emyr Jones Parry said he would submit a draft resolution which, while making the demands legally binding, would not threaten sanctions or military force.
Security Council permanent members Russia and China oppose both sanctions and the use of force.
The Iranian ambassador to the UN, Javad Zarif, told the BBC Iran was willing to find a constructive solution.
"We want to avoid confrontation but at what price? ...We are not prepared to respond to pressure," he said.
Iran 'defied warning'
Mohamed ElBaradei's report delivered on Friday said that Tehran had done little to answer questions over its nuclear intentions.
Mr ElBaradei, chief of the International Atomic Energy Agency (IAEA), told the Security Council that Iran had not halted its programme and had not given information on key issues.
This was in defiance of a Security Council warning, which gave Iran until 28 April to comply.
Among the report's findings:
- Iran's claim to have enriched low-grade uranium appears true
- Iran used undeclared plutonium in small-scale separation experiments
- Iran refused to give more information on key issues, including centrifuge programmes
NUCLEAR FUEL CYCLE
Mined uranium ore is purified and reconstituted into solid form known as yellowcake
Yellowcake is chemically processed and converted into a gas by heating it to above 64C (147F)
Gas is fed through centrifuges, where its isotopes separate and process is repeated until uranium is enriched
Low-level enriched uranium is used for nuclear fuel
Highly enriched uranium can be used in nuclear weapons
The deputy head of Iran's Atomic Energy Organisation, Mohammad Saeedi, said the IAEA report was generally acceptable.
"The report does not contain negative points. It shows that the agency still has the capacity to review Iran's nuclear case," he said, adding that Iran was ready to answer the remaining issues.
The next immediate steps will be on 2 May when negotiators from the US, Britain, France, Germany China and Russia will meet.
US Secretary of State Condoleezza Rice is to hold talks with foreign ministers of the other four permanent Security Council members and Germany on 9 May.
Iran says it has the right to peaceful nuclear technology and denies Western claims that it is seeking weapons.
Tehran has vowed to hit US targets worldwide if subjected to a US military attack.