As part of its joint efforts with the US against Iran's controversial nuclear programme, Israel has developed a sophisticated cyber-weapon aimed at preventing Tehran from making an atomic bomb, according to a media report.

The tests of the destructive 'Stuxnet' worm had occurred over the past two years at the heavily guarded Dimona complex in the Negev desert, The New York Times said.

Israel has spun nuclear centrifuges virtually identical to Iran's at Natanz, where Iranian scientists are struggling to enrich uranium, the paper quoted experts as saying.

"To check out the worm, you have to know the machines," said an American expert on nuclear intelligence.

"The reason the worm has been effective is that the Israelis tried it out."

The biggest single factor in putting time on the nuclear clock appears to be Stuxnet, the most sophisticated cyber-weapon ever deployed, the paper said.

Earlier, there had been widespread speculation that Israel was behind the worm that had attacked computers in Iran.

Recently, the retiring chief of Israel's Mossad intelligence agency, Meir Dagan, and Secretary of State Hillary Rodham Clinton separately announced that they believed Iran's efforts had been set back by several years.

Clinton cited American-led sanctions, which have hurt Iran's ability to buy components and do business around the world.

The Stuxnet worm itself now appears to have included two major components. One was designed to send Iran's nuclear centrifuges spinning wildly out of control.

Another secretly recorded normal operations at the nuclear plant, then played those readings back to plant operators, like a pre-recorded security tape in a bank heist, so that it would appear that everything was operating normally while the centrifuges were actually tearing themselves apart, the paper said.