The United States was advised to adopt a policy of "covert sabotage" of Iran's clandestine nuclear facilities, including computer hacking and "unexplained explosions", by an influential German thinktank, a leaked US embassy cable reveals.

Volker Perthes, director of Germany's government-funded Institute for Security and International Affairs, told US officials in Berlin that undercover operations would be "more effective than a military strike" in curtailing Iran's nuclear ambitions.

A sophisticated computer worm, Stuxnet, infiltrated the Natanz nuclear facility last year, delaying Iran's programme by some months. The New York Times said this week that Stuxnet was a joint US-Israeli operation.

On Monday, Iran's top nuclear negotiator blamed the US for the cyber-attack. Saeed Jalili told NBC News an investigation had found the US was involved in the attack that apparently shut down a fifth of Iran's nuclear centrifuges in November. "I have witnessed some documents that show [US participation]," he said.

Wikileaks: US advised to sabotage Iran nuclear sites by German thinktank