"Since Iran has mastered nuclear technology, the sanctions will have no effect," said Iran's chief nuclear negotiator Ali Larijani, according to the official IRNA news agency.

"Nuclear technology is a strategic technology of (Iran's) Islamic system and Iran will not take a step back," he added.

His comments came after British Prime Minister Gordon Brown warned this week that London would support a third United Nations resolution imposing sanctions against Iran if Tehran does not scale back its nuclear programme.

France, a fellow veto-wielding permanent member of the UN Security Council, has also said it is considering "additional sanctions" against Tehran.

Iran last month agreed with the UN watchdog International Atomic Energy Agency (IAEA) on a timetable to answer outstanding questions over its nuclear programme, and diplomats have said this is likely to stave off the threat of sanctions for a few more months.

But the United States, which accuses Iran of seeking an atomic weapon, has expressed great suspicion over the accord, saying the agreement does not go far enough.

The Security Council has already passed two resolutions imposing sanctions against Iran and calling on the Islamic republic to halt sensitive uranium enrichment work, something it has so far refused to do.

President Mahmoud Ahmadinejad said last week Iran had reached a key goal by putting into operation more than 3,000 uranium-enriching centrifuges, although this figure was higher than recently reported by the IAEA.

Iran insists the atomic drive is solely aimed at generating electricity and that its growing population will need nuclear power as fossil fuels start to run dry.

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