By Thomas Erdbrink
Washington Post Foreign Service
Monday, November 29, 2010; 2:23 PM
TEHRAN - Iran's uranium-enrichment program has been the target of sabotage, Iranian President Mahmoud Ahmadinejad said Monday, but he refused to say whether the Stuxnet computer virus had been responsible for the problems.
"They had been successful in making problems for a limited number of our centrifuges, with software they had installed in electronic devices," Ahmadinejad told a news conference, referring to Iran's enemies. He said the sabotage has been solved.
"Fortunately, our experts have discovered the origins of the problems, and today they [Iran's enemies] are unable to repeat these acts," Ahmadinejad said.
His acknowledgment came after a report Tuesday by the International Atomic Energy Agency said that as of Nov. 16, Iran had stopped feeding hot uranium gas into its thousands of centrifuges and that the shutdown could have lasted as long as seven days.
When asked specifically, Ahmadinejad refused to comment on whether a computer worm known as Stuxnet had been responsible.
"Write this down," Ahmadinejad said. "The Iranian president's answer to this question is: silence. That's it."
It was unclear whether Ahmadinejad was referring to the recent shutdown, reported by the IAEA, or whether he was elaborating on other problems with the controversial enrichment program.
Experts have said the computer virus was developed specifically to target the centrifuge machines at Iran's Natanz uranium-enrichment facility, which Tehran says is used to produce fuel for nuclear power plants but which the United States suspects is part of a weapons program.
Israel and the United States are seen here as the most likely sources for the cyberwarfare suggested by Stuxnet - officials in both countries have declined to comment - but Iran has denied that it was harmed by Stuxnet or that it is facing serious technical problems with its uranium-enrichment program.
Iranian Vice President Ali Akbar Salehi, who also heads the Atomic Energy Organization of Iran, acknowledged last week that Iran was the target of a computer attack, but he placed it far in the past.
"One year and several months ago, Westerners sent a virus to [our] country's nuclear sites," he said, according to the Islamic Republic News Agency.
"They intended to stop the ever-increasing progress of Iran in the nuclear field," Salehi said. "But, with the help of God, we discovered the virus exactly at the same spot it wanted to penetrate and prevented the virus from harming" any equipment.
The Institute for Science and International Security in Washington noted that Iran boosted the centrifuges in use at Natanz from 3,772 to 4,816. It also increased the number of centrifuges in six cascades, and the production has appeared to remain steady. Iran's stock of low-enriched uranium, if enriched to weapons-grade, would produce enough material for at least two nuclear weapons.
But nearly 4,000 centrifuges still sit idle at the facility, and the average monthly production of low-enriched uranium per centrifuge declined by about 10 percent, according to ISIS. Each centrifuge appeared to produce just under an ounce a month, down from 1.1 ounces, but the average number of centrifuges operating during this period is not known.
Staff writer Glenn Kessler in Washington contributed to this report.