Iran's nuclear chief said today that the malicious computer worm known as Stuxnet has not harmed the country's atomic programme and accused the West of being behind a failed sabotage attempt.

Vice President Ali Akbar Salehi's remarks came a day after diplomats told The Associated Press in Vienna that Iran's nuclear programme recently suffered major technical problems that forced the temporary shutdown of thousands of centrifuges enriching uranium the cornerstone of Iran's program.

Salehi said details about the virus became known only after Iran's "enemies failed to achieve their goals." Over the past several months, Iranian officials have acknowledged that the Stuxnet code had spread widely through Iranian industrial sites and infected several personal laptops belonging to employees at the country's first nuclear power plant.

The West has accused Iran of trying to develop a weapons capability under the cover of a civil nuclear energy program. Tehran denies the accusation, saying the programme is only for peaceful purposes and insisting it has every right under the Nuclear Nonproliferation Treaty to enrich uranium for the production of reactor fuel.

"One year and several months ago, Westerners sent a virus to (our) country's nuclear sites," Salehi said, according to the official IRNA news agency. He did not specify which sites.

"They had hoped to stop our speedy peaceful nuclear activities through software. But, with the grace of God, we discovered the virus exactly at the same spot it wanted to penetrate because of our vigilance and prevented the virus from harming (equipment)," IRNA quoted him as saying.

The diplomats who spoke to the AP in Vienna yesterday said they had no specifics on the nature of the problem that they say led Iranian experts in recent months to briefly power down the centrifuge machines they use for enrichment a nuclear technology that has both civilian and military uses.

The three senior diplomats, who are from member countries of the UN nuclear watchdog agency, spoke on condition of anonymity because the information was confidential.

Suspicions focused on the Stuxnet worm, the computer virus thought to be aimed at Iran's nuclear program, which experts last week identified as being calibrated to destroy centrifuges by sending them spinning out of control.

No one has claimed to be behind Stuxnet, but some analysts have speculated it originated in Israel.