The U.N. nuclear agency says that Iran temporarily stopped enriching uranium earlier this month for unspecified reasons.

The finding is contained in a report from the International Atomic Energy Agency released Tuesday to the U.N. Security Council and the 35 IAEA board member nations. The Associated Press obtained a copy of the restricted report.

Diplomats first told the AP of a temporary shutdown of Iran's enrichment program on Monday. They also said they did not know why the thousands of centrifuges stopped turning out material that Iran says it needs to fuel a future network of nuclear reactors.

Speculation has focused on the Stuxnet worm, which cyber experts have identified as configured to damage centrifuges.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

Iran's nuclear chief said Tuesday that the malicious computer worm known as Stuxnet has not harmed the country's atomic program 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 program 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 program 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 on Monday 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 U.N. 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.

More details on Iran's nuclear activities could be contained in a confidential update on Iran by the U.N.'s International Atomic Energy Agency — the latest report by the Vienna-based agency to its 35-nation board on its attempts to get an overview of Tehran's nuclear activities. The diplomats said it would again focus on Tehran's refusal to heed U.N. Security Council demands to stop enrichment.

Before the report's Tuesday release, diplomats told the AP in Vienna that it would also publicize an Iranian decision to reduce the planned output capacity of a new enrichment plant near the holy city of Qom.

Existence of the still-unfinished plant was unexpectedly revealed by Iran a little more than a year ago, in what the West says was an admission prompted by fears that it would soon be made public by Washington and its allies.

Iranian officials subsequently told the IAEA that the heavily fortified underground facility would have around 2,600 centrifuges. But the diplomats said Tehran recently revised plans and now envisaged fewer than 2,000 machines — a move they said could show less interest in using the facility now that its existence is known.

The resulting extra space would be used to work on centrifuge prototypes less prone to breakdown and more efficient than the present machines, said the diplomats, who asked for anonymity because their information was privileged.

According to reports released by the IAEA, Iran's uranium enrichment capacity has stagnated in recent years after initial rapid growth. Tehran has taken hundreds of centrifuges off line over the past 18 months, prompting speculation of technical problems.

At the Natanz enrichment facility in central Iran, the number of operating centrifuges declined from 4,920 in May 2009 to 3,772 in September 2010, the IAEA said.

Salehi said if the West is convinced that Iran's program has been sabotaged, then there is no need for the U.N. agency to continue to investigate the program.

"If some people believe this virus has crossed the firewall, then they should have no concern and Iran's nuclear dossier should be considered closed," Salehi was quoted as saying by another Iranian news agency, ISNA.

"But, thank God, our work ... clearly shows their failure. IAEA reports and the passage of time will prove this," he was quoted as saying.

Iran is under four sets of U.N. Security Council sanctions as well as economic and other penalties from the U.S. and some of its European allies because of its refusal to stop enriching uranium.

The technology is of key concern because, besides making fuel to run power plants, it can be re-engineered to make material for nuclear warheads.


Associated Press Writer George Jahn in Vienna contributed to this report.