Iranian President Mahmoud Ahmadinejad has again vowed never to give up Iran's nuclear programme.
Ahmadinejad has said Iran is unconcerned by UN rulings
Mr Ahmadinejad said the pursuit of peaceful nuclear technology was Iran's "absolute right... our red line".
He was speaking after the UN's atomic watchdog said Iran had failed to meet a Security Council deadline to suspend its uranium enrichment programme.
A senior Iranian official meanwhile has said Iran will allow snap checks to resume if the council drops the case.
Mohammad Saeedi, deputy head of Iran's Atomic Energy Organisation, said UN experts could conduct snap inspections of its nuclear facilities if the issue was returned to the International Atomic Energy Agency (IAEA).
However the BBC's Frances Harrison in Tehran says this is unlikely to happen , so the offer seems rather academic.
Iran halted such inspections in February after the IAEA decided to report Iran to the Security Council.
Mr Ahmadinejad was speaking after a 30-day deadline set by the Security Council for Iran to freeze its nuclear work expired without compliance.
"The Islamic republic will not negotiate with anyone on its absolute right to use peaceful nuclear technology. This is our red line, and we will never give it up," he said.
"Iran's decision to master nuclear technology and the production of nuclear fuel is irreversible."
At the same time, Dr Saeedi said Iran's uranium enrichment would continue, adding that Tehran was researching advanced designs of centrifuges, the machines used in the enrichment process.
Our correspondent says the announcement is an indication that Iran plans to press ahead with its stated intention of producing nuclear fuel on an industrial scale.
The US and EU have accused Iran of seeking to develop nuclear weapons, a charge Iran has strongly denied.
Call for action
IAEA chief Mohamed ElBaradei told the Security Council on Friday that Iran had not halted its programme and had not given information on key issues.
"After more than three years of agency efforts to seek clarity about all aspects of Iran's nuclear programme, the existing gaps in knowledge continue to be a matter of concern," he said.
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
In the wake of the report, Western powers said they will push for a legally binding UN resolution to force Iran to comply with calls for it to cease uranium enrichment.
US ambassador to the UN, John Bolton, said it was clear that Iran had accelerated its nuclear programme and that he hoped the Security Council would act swiftly.
"We do think there's a sense of urgency here and we hope that we can get council action just as soon as possible.
"We're invoking the mandatory provisions of Chapter VII [of the UN Charter]," Mr Bolton said.
Chapter VII resolutions permit enforcement by sanctions or even military action, although this step is so far highly unlikely because of opposition from Russia and China.
The BBC News website's world affairs correspondent, Paul Reynolds, says the stage is set for months of diplomatic confrontation.
The next immediate step will be a meeting of nuclear negotiators from the US, Britain, France, Germany China and Russia on 2 May.
A week later US Secretary of State Condoleezza Rice will hold talks with foreign ministers of the other four permanent Security Council members and Germany.