Sony Pictures on Wednesday cancelled the release of a madcap comedy about North Korea that triggered chilling threats from hackers, as US investigators reportedly blamed Pyongyang for a damaging cyber-raid on the movie giant.

The Hollywood studio announced the move after US theater chains said they would not screen "The Interview," about a fictional plot to assassinate North Korean dictator Kim Jong-Un.

The dramatic action came as several US media outlets reported that investigators now believe North Korea was behind the devastating cyber-attack that saw hackers gain access to a trove of internal Sony documents and unreleased movies.

Representatives for several agencies including the FBI declined to comment on the reports.

"In light of the decision by the majority of our (theater) exhibitors not to show the film 'The Interview,' we have decided not to move forward with the planned December 25 theatrical release," Sony said in a statement.

"Sony Pictures has no further release plans for the film," a spokesman added to AFP, suggesting -- though not confirming -- the film will not even be released on DVD or in other formats.

Skittishness about attending the movie followed threats by the so-called GOP (Guardians of Peace) hacking group, which invoked the September 11, 2001 attacks in an ominous warning to any movie-goers planning to see the film.

North Korea has denied involvement in the brazen November 24 cyber-attack, which some experts said could possibly have been carried out by disgruntled workers or by supporters of North Korea furious over the movie.

- N.Korea behind hack attack? -

James Lewis, a former State Department official, said that "of the characters who are out there, the most likely suspect is North Korea."

A unnamed Sony source told AFP that the suggestion that North Korea was behind it "sounds right," declining further comment.

The US State Department meanwhile sought to distance itself from the film, while defending the right to free expression.

"We're not in the business of signing off on the content of movies or things along those lines," spokeswoman Jen Psaki said.

President Barack Obama said there was "no credible evidence" of any threats linked to movie theaters.

"For now, my recommendation would be: Go to the movies," Obama told ABC News.

The National Security Council said the US government had offered Sony "support and assistance" in response to the attack.

"The U.S. government is working tirelessly to bring the perpetrators of this attack to justice, and we are considering a range of options in weighing a potential response," the NSC said in a statement.

Experts said Sony's decision sets a dangerous precedent.

"I am sympathetic with Sony and I am sympathetic with any theater that worries about damage and injury and worse involving its staff and its customers," Richard Walter of the UCLA Film School told AFP.

"But on the other hand I have to say there is something, for an American and for anybody who loves freedom, that viscerally rebels against surrendering to terror this way," he added.

"The single most disturbing aspect of this whole case it the notion that studios might cave, might surrender to lunatics of the political fringe in terms of what movies they make and what movies they release."

- 'Everyone caved. Wow' -

Actor Rob Lowe, among a number of stars who have small cameo roles in the movie, did not disguise his indignation at the Sony decision.

"Wow. Everyone caved. The hackers won. An utter and complete victory for them. Wow," he said.

"Hollywood has done Neville Chamberlain proud today," he added, in reference to the British leader's infamous appeasement of Hitler before World War II.

In addition to the threats, Sony has seen the release of a trove of embarrassing emails, scripts and other internal communications, including information about salaries, employee health records and other personal data.

On Monday, Sony Pictures boss Michael Lynton sought to reassure employees that the studio would not be destroyed by the leaks.

"This will not take us down," Lynton told employees, adding: "You should not be worried about the future of this studio."

On Tuesday, lawyers filed two class action lawsuits against Sony Pictures in Los Angeles.

One of the suits alleged that "Sony failed to secure and protect its computer systems, servers, and databases, resulting in the release of the named plaintiffs and other class members'" personal data.

"An epic nightmare, much better suited to a cinematic thriller than to real life, is unfolding in slow motion for Sony's current and former employees," the 45-page lawsuit said.