TEHRAN (AFP) – Supreme leader Ayatollah Ali Khamenei said on Tuesday that Iran will reject any dialogue if its outcome is pre-determined by Washington, raising the possibility a mooted nuclear fuel deal may be derailed.

Khamenei’s comments came as world powers turned up the heat on Iran to accept the UN-brokered nuclear deal, with US Secretary of State Hillary Clinton saying Iran was at a “pivotal moment” to show it did not want to be isolated from the international community.

Iran is engaged in high-profile UN-hosted talks with world powers over how to procure nuclear fuel for a Tehran research reactor.

But officials here are increasingly opposed to the proposed deal under which Iran would send low-enriched uranium (LEU) abroad for conversion into fuel for the Tehran reactor. They say they would rather buy the fuel directly.

On Tuesday, Khamenei, Iran’s all-powerful leader who has the final say in all national issues, raised the possibility the UN-brokered deal may fail.

“We do not want any negotiation, the result of which is pre-determined by the United States,” Khamenei said in a speech on the eve of Wednesday’s 30th anniversary of the US embassy seizure by radical students.

World powers led by Washington are backing the deal as they want to take out Tehran’s stock of LEU which they fear could be further enriched by Iran on its own to very high levels and used in making atomic weapons.

Tehran denies any ambition to develop a weapons capability.

Iran’s uranium enrichment work is the most controversial aspect of its nuclear programme. At low purity the material can be used as fuel for reactors, but in very highly enriched form it can form the fissile core of an atom bomb.

Khamenei said that giving the United States a veto over the nuclear talks would be like a “sheep and wolf relation which the late imam (Ayatollah Ruhollah Khomeini) has said that we ‘do not want'”.

Khomeini, who led the 1979 Islamic revolution which toppled the US-backed shah, opposed any dialogue with Washington that was not on an “equal footing.”

On Monday, Foreign Minister Manouchehr Mottaki called for a review of the nuclear proposals under which Iran would ship out 75 percent of its LEU stocks.

But French Foreign Minister Bernard Kouchner warned that the six world powers negotiating with Iran would not tolerate delaying tactics.

“If the Iranian response is to stall, as it seems to be, we will not accept this,” he told journalists in Paris.

Clinton said: “This is a pivotal moment for Iran.

“Acceptance fully of this proposal would be a good indication that Iran does not wish to be isolated and does wish to cooperate.”

Khamenei’s comments came as Iran prepared to mark the seizure of the US embassy 30 years ago that sparked the rupture of relations with Washington. Islamist students held 52 US diplomats for 444 days.

The commemoration has become one of the cornerstones of the Islamic regime and every year students gather outside the embassy building in central Tehran and shout “Death to America!” and “Death to Israel!”.

Officials have expressed concern that critics of hardline President Mahmoud Ahmadinejad may try to turn this year’s rally into a new protest against his controversial re-election in June.

In a veiled warning to the opposition, Khamenei said those with “ill-intentions” against the regime will not be allowed to “throw down the red carpet to the United States.”

The main opposition leader Mir Hossein Mousavi has hinted that a protest rally could be held on Wednesday, while Iranian authorities have warned they will crack down on any protests.