Iran's parliament stressed Wednesday that Tehran will not back down from its nuclear "rights" in talks with world powers -- but softened its stance on the key thorny issue of higher-level uranium enrichment.

Parliamentary speaker Ali Larijani said lawmakers were instructing Iran's negotiators "they don't have the right to make concessions on Iran's rights under the NPT (nuclear Non-Proliferation Treaty)."

"Nevertheless, concerning the level of uranium enrichment, Iran can define it according to its needs and desires, but that cannot be a rule limiting Iran's nuclear activities," he said.

Although several Iranian officials, including President Mahmoud Ahmadinejad, Foreign Minister Ali Akbar Salehi and Iran nuclear energy chief Fereydoon Abbasi Davani, have all previously said the issue of enriching uranium to 20 percent could be open to negotiation, it was the first time the parliament has done so.

Iran's stockpile of 20-percent enriched uranium is the priority issue at the next round of talks due to take place next Monday and Tuesday in Moscow, following two unproductive rounds in Istanbul and Baghdad earlier this year.

Iran says it needs uranium enriched to 3.5 percent to fuel its sole nuclear energy plant in Bushehr, and 20 percent to produce medical isotopes in its Tehran research reactor.

But Western nations fear that, with just a few months more of processing, the 20-percent stock could be enriched to the 90-percent level used in to make atomic bombs.

Iran's legislature has in recent years been one of Iran's most hardline institutions in resisting UN Security Council demands that all of Tehran's enrichment be suspended.

Its members hew closely to the line espoused by Iran's supreme leader, Ayatollah Ali Khamenei, who is the ultimate authority on Iran's nuclear and foreign policy decisions.

Larijani made his comments during an appearance in parliament by Iran's chief negotiator and Khamenei's representative in the nuclear talks, Saeed Jalili.

Jalili reiterated Iran's official message to the so-called P5+1 group of powers it is negotiating with (UN Security Council permanent members the United States, Britain, France, Russia and China, plus non-permanent member Germany).

He insisted Iran's uranium enrichment was for peaceful purposes and highlighted the fact that Khamenei had issued an edict banning all weapons of mass destruction.

He also said that "our enrichment is proportionate to our needs" and stressed that the country's two enrichment plants, at Natanz and Fordo, were under the supervision of the International Atomic Energy Agency.

"The issue of enrichment to 20 percent or higher has been raised," he said.

Sanctions imposed by the UN Security Council and by the West had failed to stop Iran progressing with its nuclear ambitions, he said.

Jalili added that covert acts against Iran attributed to the West had not succeeded in thwarting Tehran from realising its nuclear ambitions.

"All sorts of physical acts and even malware have failed," he said, apparently referring to the assassination of four nuclear scientists in recent years and the discovery of several computer viruses attacking Iran's nuclear networks.