Oscar winner Alex Gibney said Wednesday he hopes his new documentary "Zero Days" exposing the secret scope of the US cyber warfare programme will "rattle some cages" to trigger a debate about a global IT arms race.

"Zero Days", premiering in competition at the Berlin film festival, cites intelligence sources as saying the United States and Israel developed a much broader plan for cyber operations against Iran than originally thought.

Iran's nuclear refining facilities were temporarily hobbled in 2010 by a virus called Stuxnet, which is suspected to have been developed by the United States and Israel, although neither government has acknowledge it.

It was believed to be the first virus designed not just to steal information or hijack computers, but to damage equipment.

However Gibney's film quotes anonymous CIA and NSA operatives describing a covert cyber operation called "Nitro Zeus" that would have gone much further, harming Iranian civilian and military infrastructure if diplomatic efforts to curb its nuclear programme had failed, prompting a military conflict.

The contingency plan using malware was put in place in case Israel launched a unilateral strike against Iran, drawing the United States into a war, according to Gibney's sources.

Any cyber attack, which could be carried out without any "boots on the ground", would require personal authorisation by the US president.

According to the film, "Nitro Zeus" was put on ice after Iran and the permanent five members of the UN Security Council plus Germany agreed last July to have sanctions lifted in return for Tehran ensuring its nuclear programme remains for civilian use.

- 'Incredible amount of secrecy' -

Gibney, 62, is best known for the 2007 Academy Award-winning "Taxi to the Dark Side" about the US military's use of torture, his 2013 film "We Steal Secrets: The Story of WikiLeaks" and last year's "Going Clear: Scientology and the Prison of Belief".

He and his team made use of documents published by WikiLeaks and former NSA contractor Edward Snowden for "Zero Days".

Gibney also conducts on-camera interviews with high-profile subjects including former CIA and NSA director Michael Hayden who, without confirming any classified programmes, complains of a "hideous" lack of transparency blocking a public discussion of cyber warfare.

One source describes Stuxnet, which the film says Britain also cooperated on, as having worked in a "subtle" way, keeping even Iran in the dark about its impact.

However, the film argues that Israel grew increasingly fearful of Iran's nuclear ambitions and unilaterally deployed the "worm" in a more aggressive way, exposing the programme and triggering retaliatory measures including an Iranian cyberattack on the Saudi state oil company and several US banks.

"Our friends in Israel took a weapon that we jointly developed -- in part to keep Israel from doing something crazy -- and then used it on their own in a way that blew the cover of the operation and could have led to war," the source says.

The film calls for dialogue about a new doctrine that would establish ground rules for waging battle with computer "worms" and malware, much like the debate conducted after World War II on atomic weapons.

"There hasn't really yet been a discussion of how formidable the offensive cyber programme of the United States is and presumably also (those of) Israel, Russia, China and these are weapons that in effect are being implanted and crisscrossing the world," he said.

He blamed the Obama administration for rampant classification of its capabilities and "aggressively pursuing leaks" which he said had had a chilling effect.

"I am angry about the incredible amount of secrecy in the United States and how it's become a kind of obsession that is damaging our democracy," Gibney told reporters after a well-received press screening ahead.

"I hope it (the film) is a cry to arms, I hope we rattle some cages."

"Zero Days" is among 18 contenders for the festival's Golden Bear top prize, to be awarded by jury president Meryl Streep on Saturday.