"The right to enrichment within the framework of the nuclear Non-Proliferation Treaty (NPT) and under the surveillance of the International Atomic Energy Agency (IAEA) is an absolute right," Elham said at his weekly press briefing.

"Based on the NPT, even the right to enrich uranium is non-negotiable, and Iran believes that access to peaceful nuclear technology is an indisputable and irreversible right of the nation," he added.

"This right and its implementation must be guaranteed. This is not something on which we can back down, whether for research or industrial purposes. This is not something on which we can negotiate or back down," Elham stressed.

The government spokesman's remarks were seen as another reject of a European Union offer of a package of incentives to Tehran in return for a halt to its sensitive nuclear activity.

In a hope to persuade Iran to halt fuel cycle work, the EU trio of Britain, France and Germany are planning to offer Tehran a package of trade, technology and security incentives.

But U.S. Secretary of State Condoleezza Rice said on Sunday the European powers had not asked Washington to provide Iran with security guarantees.

The European proposals are to be discussed at a meeting in London on Wednesday by the five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- along with Germany.

Referring to the upcoming London meeting on Wednesday, Elham urged the participants of the talks to "take into consideration Iran's legitimate rights in the nuclear field" when making decisions on the nuclear issue.

If Tehran does not accept the deal, sanctions could follow --including an arms embargo, political and economic measures, a visa and travel ban on selected high-ranking officials and a freeze of assets of individuals and organizations connected to the Iranian government.

But Iranian top officials have on many occasions underlined that Tehran would not accept the European offer.

Iranian President Mahmoud Ahmadinejad has ridiculed the European offer as "giving us walnuts and chocolates in exchange for our gold."