Iran will not bow to outside pressure to abandon its nuclear technology, President Mahmoud Ahmadinejad has said.
Iran says its nuclear programme is for purely peaceful purposes
"We have obtained the technology for producing nuclear fuel... no-one can take it away from our nation," he said.
He was speaking on the eve of a crucial report by the UN's nuclear watchdog on whether Iran has met its demands and stopped uranium enrichment.
US Secretary of State Condoleezza Rice has said the UN Security Council must be prepared to act over Iran.
The Council's credibility was on the line over how it dealt with Iran, Ms Rice said in the Bulgarian capital, Sofia, where she is attending a meeting of Nato foreign ministers.
"The Security Council is the primary and most important institution for the maintenance of peace and stability and security and it cannot have its word and its will simply ignored by a member state," she said.
Her call was backed by French Foreign Minister Philippe Douste-Blazy, who said the world had to show "unity and firmness" towards Iran.
"The situation is serious and worrying," he said, "there is nothing to suggest that Iran is conforming to the demands of the international community."
No giving in
In a defiant speech to a crowd in Zanjan in north-west Iran, President Ahmadinejad said Iran would not give in one iota to "oppression".
"If you think by frowning at us, by issuing resolutions... you can impose anything on the Iranian nation or force it to abandon its obvious right, you still don't know its power," he said, his speech carried live on state television.
The UN Security Council demanded on 29 March that Iran comply with the demands of the IAEA for a "full and sustained suspension" of its uranium enrichment work.
Mohammed ElBaradei, the head of the UN's nuclear watchdog, the IAEA, is due to report back on Friday as to whether Iran has complied with those demands.
The US, which argues that Iran is trying to acquire nuclear weapons, is trying to rally support from the Security Council for tougher action against the Tehran government, including sanctions.
Washington has not ruled out the possibility of military strikes.
Calls for restraint
Iran says it has the right to peaceful nuclear technology and denies Western claims that it is seeking weapons.
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
China and Russia, who are both veto-holding members of the Security Council, are opposed to sanctions and have urged restraint from all sides.
Russian President Vladimir Putin said the IAEA needed to continue to play a key role in the crisis.
"We believe it is the IAEA that must play a key role and not have this weight unloaded on to the back of the Security Council," Mr Putin said.
In Beijing, Chinese foreign ministry spokesman Qin Gang issued an appeal for calm.
"We hope the relevant parties can keep calm and exercise restraint so as to avoid moves that would further escalate the situation," Mr Qin said.
He said the problem could still be "resolved through dialogue and diplomatic means, which is the correct choice for all parties concerned".