In a speech marking the 18th anniversary of the death of Iran's revolutionary founder Ayatollah Ruhollah Khomeini, Khamenei scoffed at the notion of Iran "begging" to Western powers to allow its nuclear drive to continue.

"The only way for a nation to realise its rights is vigilant resistance. They should be alert, recognise their rights and insist on it," Khamenei told thousands packed into Khomeini's shrine in the southern outskirts of Tehran.

"A nation that wants to reach independence must pay a price. If it wants to preserve its rights against bullies, then it has to pay a price," said Khamenei to chants of "nuclear energy is our natural right" and "death to America".

"It cannot sit in a corner and expect development and progress," he added.

Khamenei's speech comes at a crucial moment in the crisis over Iran's nuclear programme, with the United States and Western powers pushing for a third set of UN sanctions to punish Tehran for its nuclear defiance.

Iran has infuriated the West by refusing to suspend uranium enrichment, a process Europe and the United States fear could be used to make nuclear weapons and want Tehran to suspend immediately.

"Iranians should not beg for their right to obtain nuclear energy. They should not beg to the domineering world powers. This is not the way of an independent and free nation," Khamenei added.

The United States accuses Iran of seeking nuclear weapons, a charge vehemently denied by Tehran, which says it wants only to generate energy. Washington has never ruled out the use of force to make Iran heed the Security Council's ultimatum.