"That is something that Iran will not accept and Iran strongly resisted it in negotiations in Paris" with European states last month, Hossein Moussavian, was quoted as saying by the Tehran Times.
Moussavian said the talks on July 29 and 30 "had reached a very complicated and difficult stage" but added that "the negotiators are determined to continue their talks."
The Europeans had told Iran "we recognise your right to possess peaceful (nuclear technology) and we give an international guarantee to provide you with nuclear fuel and facilitate your efforts to gain access to nuclear technology," he said.
But they had added that "since the fuel cycle in Iran may be diverted toward a nuclear weapons program in the future, we want you to relinquish it as a confidence building measure."
This was unacceptable to Tehran, Moussavian said.
On Wwednesday Iran's Foreign Minister Kamal Kharazi asserted the Islamic republic had a "legitimate right" to enrich uranium, the most sensitive part of the nuclear fuel cycle that the country is under pressure to abandon.
"We will lobby for our rights in the international community to deal with the negative atmosphere our enemies have created against Iran," Kharazi was quoted as saying by the state news agency IRNA.
"We will never allow the enemy to trample upon our legitimate rights enshrined in the international conventions," he added.
The European Union's "big three" -- Britain, France and Germany -- have been pressing Iran to cease working on the nuclear fuel cycle in exchange for increased trade and cooperation and the guaranteed supply of nuclear fuel from abroad.
Such work is permitted under the nuclear Non-Proliferation Treaty (NPT), but the concern is that once fully mastered, a country possessing such technology can easily divert it into military usage.
Many diplomats believe that even if Iran may not be working on nuclear weapons now, it would like to have the option in the future. Iran denies charges it is seeking to develop a nuclear bomb.
Iran has agreed to temporarily suspend enrichment pending the completion of an International Atomic Energy Agency (IAEA) probe, but is working on other parts of the fuel cycle and has recently resumed making centrifuges used for enrichment.
"There has been absolutely no agreement that Iran would stop enriching uranium, since enrichment is our legitimate right," Kharazi said.
"We will continue negotiations with the European countries, the International Atomic Energy Agency and members of the Non-Aligned Movement (NAM)," he added.
US Secretary of State Colin Powell said last month that it was "more and more likely" that Iran would be referred to the UN Security Council by the IAEA as a possible prelude to sanctions.
The United States has accused Iran of wantonly flouting international calls to curb its nuclear activities, saying Tehran is engaged in a "direct challenge" to the UN's nuclear watchdog.