By Miranda Eeles
BBC correspondent in Tehran
Iranian President Mohammad Khatami says his country does not need permission to pursue a civilian nuclear programme, and will not stop doing so.
Iran has been accused of keeping some of its nuclear activities secret
Mr Khatami's comments come amid mounting pressure on Iran by the US ahead of an International Atomic Energy Agency (IAEA) meeting in Vienna next month.
Washington believes Tehran is secretly building nuclear weapons.
It wants the IAEA to refer Iran to the UN Security Council for breaching the Nuclear Non-proliferation Treaty.
Tehran denies the allegations, saying its programme is peaceful and for generating electricity.
Speaking after a cabinet meeting in Tehran, President Khatami said threats to send its nuclear case to the Security Council would not prevent Iran from pursuing nuclear technology.
He said if anyone wanted to deny the country that right, Iran would be willing to pay the price.
He added that due to its Islamic ideological beliefs, Iran could not acquire nuclear weapons.
Mr Khatami's statement comes after US officials recently expressed growing confidence that international resolve was hardening against Tehran.
Last month Iran declared it had resumed building nuclear centrifuges, angering Britain, Germany and France, who have tried to broker a diplomatic solution.
This reneged on an agreement made last year with the three countries obliging Iran to suspend all enrichment activities.
Both sides, however, are showing signs of strain. Many in Iran's new conservative-dominated parliament have accused the government of conceding too much to the Europeans.
More than three-quarters of the Majlis (parliament) signed a draft bill on Wednesday that would oblige the government to continue its pursuit of peaceful nuclear technology.
Iran's claim that it does not have a secret nuclear weapons programme was boosted by reports earlier this week that UN nuclear inspectors had traced weapons grade uranium found in Iran to imported equipment brought in from Pakistan.