WASHINGTON: US and Israeli intelligence services collaborated to develop a destructive computer worm to sabotage Iran's efforts to make a nuclear bomb, The New York Times reported Sunday.

The newspaper quoted intelligence and military experts as saying Israel has tested the effectiveness of the Stuxnet computer worm, which apparently shut down a fifth of Iran's nuclear centrifuges in November and helped delay its ability to make its first nuclear weapons.

The testing took place at the heavily guarded Dimona complex in the Negev desert housing the Middle East's sole, albeit undeclared nuclear weapons program. Experts and officials told the Times the effort to create Stuxnet was a US-Israeli project with the help, knowingly or not, of Britain and Germany.

“To check out the worm, you have to know the machines,” a US expert told the newspaper. “The reason the worm has been effective is that the Israelis tried it out.”

There has been widespread speculation Israel was behind the Stuxnet worm that has attacked computers in Iran, and Tehran has blamed the Jewish state and the United States for the killing of two nuclear scientists in November and January.

The Times report came as Iran earlier said its controversial uranium enrichment program was progressing “very strongly,” just days ahead of a high-profile meeting between Tehran and six world powers over the Islamic republic's nuclear program.

Both the United States and Israel have recently announced they believe the program has been set back by several years. US Secretary of State Hillary Clinton pointed to a series of sanctions imposed since June 2009 by the UN Security Council and individual countries.

And Moshe Yaalon, Israel's strategic affairs minister and former military chief, said last month that a series of “technological challenges and difficulties” meant Tehran was still about three years away from being able to build nuclear weapons.

Israel has backed US-led efforts to prevent Iran from developing a nuclear weapons capability through sanctions, but has also refused to rule out military force.