Iranian President Mahmoud Ahmadinejad has said Iran will defend its nuclear programme to the end, and must not show weakness "in front of the enemy".
Mr Ahmadinejad said the Iranian people would defend their rights
His comments came a day after the UN nuclear body confirmed Iran had ignored a deadline to stop uranium enrichment.
Permanent UN Security Council members and Germany will meet on Monday to discuss further sanctions against Iran.
The head of the UN nuclear agency, the IAEA, has said there is still "a window of opportunity" for negotiations.
The UN Security Council had given Iran until 21 February to halt uranium enrichment.
But the IAEA concluded in a report on Thursday that Iran was expanding rather than halting its enrichment programme, defying a UN resolution of December 2006.
Speaking after meeting UN Secretary General Ban Ki-moon in Vienna, IAEA head Mohamed ElBaradei said he believed a diplomatic solution could still be reached.
"The door is still open, there is a window of opportunity for both Iran and the international community to go back to the negotiating table," he said.
"I believe this is the way for a long-term solution."
Mr Ban called on Tehran to comply with the UN Security Council resolution and make greater efforts to show it sought nuclear technology for purely peaceful purposes.
"I would again urge Iranian authorities to engage in dialogue with the international community through peaceful means," he said.
Iran says the UN call for it to stop uranium enrichment is unacceptable as it has no legal basis.
POSSIBLE NEXT STEPS
New UN resolution on tougher economic sanctions, tabled by US or European allies
US pressure on Europeans to step up bilateral sanctions
New initiative to get Iran back to talks
"The Iranian people are vigilant and will defend all their rights to the end," Iranian news agency Isna quoted Mr Ahmadinejad as saying, at a rally in northern Iran.
"If we show weakness in front of the enemy the expectations will increase but if we stand against them, because of this resistance they will retreat."
In a Friday prayers sermon broadcast on state radio, former Iranian President Akbar Hashemi Rafsanjani also said threats of further sanctions would not work.
"They will not get a result this way, it will just make problems for themselves, the world and especially our region," he said.
He said Iran was willing to give Western powers "the necessary guarantees" if they returned to the negotiating table.
Representatives of the five permanent Security Council members - the US, UK, France, Russia and China - plus Germany will meet in London for talks on drafting a second resolution sanctioning Iran on Monday.
German Chancellor Angela Merkel, speaking at a press conference with French President Jacques Chirac on Friday, said the door "remains open" for negotiations with Tehran.
But, she said, the report made clear Iran was not fulfilling its obligations and therefore it was right to return to the UN Security Council.
Meanwhile Chinese Foreign Minister Li Zhaoxing has telephoned his Iranian counterpart to express Beijing's desire "to peacefully resolve" the nuclear issue, China's state news agency Xinhua says.
US Undersecretary of State Nicholas Burns, who will take part in the talks, said Iran was "effectively thumbing its nose at the international community".
Tehran denies Western claims it is secretly trying to build nuclear arms, saying its nuclear programme is for purely peaceful, energy-producing purposes.
While enriched uranium is used as fuel for nuclear reactors, highly enriched uranium can also be used to make nuclear bombs.