Iran's regime on Thursday underlined its message that Western powers must recognise Tehran's "right" to uranium enrichment if upcoming talks in Moscow are to advance.

Two key officials with top advisory positions to Iran's supreme leader, Ayatollah Ali Khamenei, stressed that line in media reports a day after other officials claimed that the West was not showing enough willingness to negotiate.

Ali Akbar Velayati, Khamenei's top adviser on foreign policy, said in a Fars news agency report that the world powers involved in the Moscow talks needed to adopt a "realistic" approach on "Iran's just rights".

Akbar Hashemi Rafsanjani, a former president who now chairs the Expediency Council that advises Khamenei, said, according to the Mehr news agency: "The West must realise the path to success in talks is through acceptance of Iran's just (nuclear) right."

Rafsanjani, seen as a pragmatic voice in the regime, added that the recurring use of Western "threats, sanctions and pressure must also be refrained from."

Those tactics, he said, were getting in the way of a "win-win scenario" in Moscow.

The language used by both men alluded to Iran's enrichment of uranium, which Tehran says is permitted under the nuclear Non-Proliferation Treaty to power nuclear energy plants and to produce medical isotopes.

Despite Tehran's repeated denials, Western powers suspect the uranium is being enriched to give Iran a "break-out" capability to make atomic weapons.

The United States, its allies Britain, France and Germany, as well as Russia and China, form the P5+1 group which is negotiating with Iran on the sensitive nuclear issue.

All but Germany are permanent members of the UN Security Council, which has since 2006 issued a slew of resolutions demanding that Iran halt all enrichment.

They have imposed a raft of UN sanctions, which the United States and the European Union have added to with their own harsh measures against Iran's economy.

But two rounds of largely fruitless negotiations this year, in Istanbul and Baghdad, have left the talks with no breakthrough. The next round, in Moscow on June 18-19, is seen as crucial in determining whether any ground at all exists for a diplomatic solution.

On Wednesday, Iranian President Mahmoud Ahmadinejad accused the P5+1 of setting out to "waste time" in the Moscow meeting, while Iran's top nuclear negotiator, Saeed Jalili, also said he doubted the willingness of world powers to see the Moscow talks succeed.

And on Thursday, speaking in Beijing on the sidelines of a regional security summit, Ahmadinejad said Iran wanted to pursue talks with the superpowers, insisting that Tehran was not seeking to make an atomic bomb.

"The Iranian people are committed to the negotiations but the superpowers don't seem to want to find a solution... and probably they will not allow for a solution to be found in Moscow," ISNA news agency quoted Ahmadinejad as saying in Beijing.

"If Iran wanted to build a bomb, it would not be afraid to say so and no one will be able to stop it... but the Islamic republic's policies and principles do not allow the country to seek atomic weapons," he added.

Khamenei and other Iranian officials have repeatedly said in recent months that making, owning and using atomic weapons is "haram" (forbidden) in Islam, and stress that Tehran only wants to use nuclear energy for peaceful means.

Iran's envoy to the UN atomic watchdog, Ali Asghar Soltanieh, said that "Iran will not for one second freeze enrichment."