But he stressed that Iran still faced other obstacles before it could build a weapon.

While Iran is "probably" on track to hit a target of producing 3,000 centrifuges -- the machines which enrich uranium -- at its nuclear facility in Natanz by the end of March, installing them and making them function properly would be complicated, Chipman said.

"If and when Iran does have 3,000 centrifuges operating smoothly, the IISS estimates it would take an additional nine to 11 months to produce 25 kilogrammes (55 pounds) of highly enriched uranium, enough for one implosion-type weapon.

"That day is still two to three years away at the earliest," he said.

Launching the IISS's annual report assessing global military capability, Chipman added that the "main bottleneck" for producing weapons was learning how to run UF6 through linked cascades for long periods.

"If Iran overcomes the technical hurdles, the possibility of military options to stop the programme will increase," he added.

Although US President George W. Bush has said the United States has no plans to invade Iran, Washington is isolating the Iranian regime over nuclear suspicions and allegations of complicity in attacks on US troops in Iraq.

In December, the United Nations Security Council adopted a resolution imposing sanctions on Iran for its repeated refusal to freeze enrichment work.

President Mahmoud Ahmadinejad's regime insists it only wants to use nuclear technology to generate energy, despite fears that it could be used to build an atomic bomb.

Chipman said that the sheer volume of centrifuges was "a political act, designed to demonstrate technological achievement at home and defiance abroad."

He added that having such a high number in place could provide Iran with a bargaining chip if international negotiations resume.

"Having more centrifuges in place -- even if not operating -- would also put the programme at a higher plateau in the event negotiations resumed and Iran made an offer to cap the size," he added.

Iran kicks off 10 days of celebrations Thursday marking the anniversary of its 1979 Islamic revolution, during which it is thought officials may announce the start of phase one of nuclear fuel production for industrial purposes.

But it could face further sanctions later this month when Mohamed ElBaradei, director general of the International Atomic Energy Agency, submits a compliance report to the UN Security Council.

Elsewhere in his speech, Chipman lent his voice to those criticising Bush's troop surge to Iraq, which will see an extra 21,500 military personnel deployed mainly to Baghdad.

"Simply flooding one area of Iraq, in this case parts of Baghdad, with troops, neglects the subtler aspects of counter-insurgency doctrine," he said.

"For a surge in troops to be sustainable, it has to be married with the second stage of the process."

This meant building up administrative capacity and establishing the rule of law, he added.

earlier related report
Iran celebrates revolution vowing nuclear advance
Tehran (AFP) Jan 31 - Iran kicks off 10 days of celebrations on Thursday marking the anniversary of the 1979 Islamic revolution, with officials promising the unveiling of a major advance in its controversial nuclear drive.

The festivities known as the "Decade of Fajr" (Dawn) culminate on February 11, the date 28 years ago when the US-backed Shah's regime fell to revolutionaries led by the late supreme leader Ayatollah Ruhollah Khomeini.

President Mahmoud Ahmadinejad has already said he will announce "good news" about the development of the nation's nuclear programme during the anniversary celebrations.

Iran has defied the international community and vowed to press on with its nuclear work despite a UN resolution in December imposing sanctions over its refusal to suspend uranium enrichment.

Enrichment is the focus of Western fears that Tehran is seeking to build nuclear weapons as the process can make the fissile core of an atom bomb as well as nuclear fuel.

Iran, OPEC's second largest oil exporter, insists it has the right to nuclear technology as a signatory to the Non-Proliferation Treaty and that its programme is purely designed to generate energy.

The "Decade of Fajr" begins at 9:33 (0603 GMT) on Thursday, the exact time Khomeini landed at Tehran airport, making a triumphant return from exile in France greeted by massive crowds of fervent supporters.

As the clock strikes that minute, school and churches bells will toll, train and ship horns will be sounded and factory sirens wail.

Flowers will also be laid at Khomeini's shrine in southern Tehran in the main cemetery where many of Iran's war dead are buried.

Akbar Hashemi Rafsanjani, Iran's former president and the current head of its powerful arbitration body, will make a speech at the shrine, which marks the spot where Khomenei told throngs of his revolutionary supporters about the creation of an Islamic regime.

Iran's outspoken populist president is then expected to make a speech on February 11 in the captial's main Azadi (Freedom) square, where a 100-strong orchestra will play a "nuclear symphony".

"Iranian people, with faith in God, wisdom and resistance, will defend their inalienable rights... and celebrate the realization of their peaceful nuclear rights during Fajr," Ahmadinejad said Wednesday.

"The country's overall policies are decided by the supreme leader and the government has to apply them. The president, who heads the executive power, announces our nuclear position," said Ahmadinejad, who has faced increasing domestic criticism over his handling of the nuclear issue.

In December, deputy foreign minister Mehdi Mostafavi was quoted as saying that the first phase of production of nuclear fuel for industrial needs would commence during Fajr.

Iran is planning to increase its enrichment capacity by installing 3,000 centrifuges, the machines which enrich uranium, at an underground facility in Natanz.

It is already running two pilot cascades of 164-centrifuges each in Natanz, allowing for an enrichment capacity that is currently low and research-oriented.

However, there have been conflicting reports about whether the extra centrifuges have already been installed.

Iranian leaders have so far have not shown any intention of yielding to demands of UN resolution 1737 and suspending enrichment despite a call by UN nuclear watchdog chief Mohamed ElBaradei for a "timeout" in the showdown.

Iran could however face more sanctions after February 21 when ElBaradei, director general of the International Atomic Energy Agency, is due to submit a report on its compliance to the UN Security Council.

earlier related report
Iran denies North Korea's nuclear assistance
Moscow (RIA Novosti) Jan 31 - Iran dismissed Wednesday media reports of its nuclear cooperation with North Korea. Last week, Russian media quoted Britain's Daily Telegraph as saying that Pyongyang was assisting the Islamic Republic in preparing an underground nuclear test, similar to the one that North Korea conducted last October, provoking international condemnation.

"Such unsubstantiated reports are printed with the sole purpose of misleading public opinion about Iran's positive actions on the nuclear issue, as well as Iran's rights arising from the Nuclear Non-Proliferation Treaty," the Iranian Embassy to Moscow said in a statement.

The diplomatic mission insisted that talented young Iranian scientists learned how to enrich uranium for peaceful ends on their own, and that Tehran has repeatedly demonstrated the transparency of its nuclear activities to the International Atomic Energy Agency, the UN nuclear watchdog.

Iran has been the source of international concerns since it resumed uranium enrichment a year ago, which some Western countries suspect is part of a covert nuclear weapons program, although Tehran has consistently denied the allegation.

In response to Iran's unwillingness to give up its nuclear ambitions, the UN Security Council adopted a resolution in December with sanctions against Iran that banned activities involving uranium enrichment, chemical reprocessing, heavy water-based projects, and the production of nuclear weapons delivery systems.

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