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.

A diplomatic cable sent by the US ambassador to Germany, Philip Murphy, in January 2010, records that Perthes said a policy of "covert sabotage (unexplained explosions, accidents, computer hacking etc) would be more effective than a military strike, whose effects in the region could be devastating".

Perthes is a leading western expert on Iran. An earlier diplomatic cable, sent by Murphy on 14 December 2009 showed that his advice was heeded by politicians and officials - including Condoleezza Rice, the former US secretary of state.

"The majority of the guests at the table distinctly deferred to Perthes for guidance on where the Iran issue might be headed or should be headed," Murphy wrote. "This was striking amongst such a high ranking group of people operationally involved with the Iran issue."

In an interview with the Guardian, Perthes said the ambassador accurately reflected his view "that 'unexplained accidents' or 'computer failures' etc are certainly better than military strikes. And that military strikes – a military escalation with Iran – must be avoided.

"Compared to military action, such acts have the advantage that the leadership of a country that is affected wouldn't need to respond – everybody can agree that there was a technical failure, no one needs to shoot or bomb. And at the same time, everybody has understood the message – about what developments are unacceptable to the other side.

"My sense at the beginning of 2010 was – without having any specific knowledge – that some countries were indeed preparing to slow down the Iranian nuclear programme by acts of sabotage, or computer hacking."

US and Israeli officials refused to comment on their reported involvement with Stuxnet yesterday. However, the leaked cables show that more covert methods of infiltrating Iran's nuclear programme – including powerful cyber attacks – was a proposal gaining traction inside US diplomatic circles last year.

President George Bush approved $300m (£189m) on joint covert projects aimed at Iran, understood to have included Stuxnet, before leaving office in 2009.

The chances of a military strike against Iran are now understood to be receding, in part because of the success of the Stuxnet cyberattack, but also due to the assassination last year of two Iranian nuclear scientists, which was attributed to Israel.

Stuxnet wiped out roughly a fifth of the centrifuges used to enrich uranium at Iran's Natanz base around August last year. Security experts told the Guardian at the time that Stuxnet was "the most refined piece of malware ever discovered", raising suspicion that it was a well-funded and potentially state-sponsored operation. According to the New York Times, the Stuxnet worm was tested at a secret Israeli bunker at Dimano, near the Negev desert.