U.S. President Barack Obama ordered stepped-up cyberattacks on Iran's nuclear program months after taking office, significantly expanding America's first sustained use of cyberweapons, The New York Times reported on Friday.

The program, launched by the Bush administration and code-named Olympic Games, targets the computer systems that run Iran's main nuclear enrichment facilities, the paper said.

However, a programming error allowed the worm, Stuxnet, which was developed by the United States and Israel, to escape Iran's Natanz plant and go around the world on the Internet in the summer of 2010.

Obama decided to press ahead with the program after seeing evidence that it was still causing havoc for the Iranians. In the following weeks, the Natanz plant was hit by a newer version of the computer worm, and then another after that.

"The last of that series of attacks, a few weeks after Stuxnet was detected around the world, temporarily took out nearly 1,000 of the 5,000 centrifuges Iran had spinning at the time to purify uranium," the Times said.

The Times based its report on interviews over the past 18 months with current and former American, European and Israeli officials involved in the program, as well as a range of outside experts.

These officials gave differing assessments of how successful the sabotage program was in slowing Iran's progress toward developing the ability to build nuclear weapons.

"Internal Obama administration estimates say the effort was set back by 18 months to two years, but some experts inside and outside the government are more skeptical, noting that Iran's enrichment levels have steadily recovered, giving the country enough fuel today for five or more weapons, with additional enrichment," the Times said.

It said the U.S. government only recently acknowledged developing cyberweapons, and it has never admitted using them. There have been reports of one-time attacks against personal computers used by members of al-Qaida, and of contemplated attacks against the computers that run air defense systems, including during the NATO-led air attack on Libya last year.

Olympic Games was of an entirely different type and sophistication.

"It appears to be the first time the United States has repeatedly used cyberweapons to cripple another country's infrastructure, achieving, with computer code, what until then could be accomplished only by bombing a country or sending in agents to plant explosives," it said.

Iran agreed to meet again in Moscow on June 18-19 with the six powers -- the United States, Britain, France, Russia, China and Germany, over its disputed nuclear program, following two rounds of talks respectively in April and in May.

Iran insists on the peaceful nature of its nuclear program, while the Western countries say it is a cover for developing nuclear weapons.