BOSTON (REUTERS, AFP) - US investigators have determined that North Korea was behind the cyber attack on Sony Corp's computers, US government sources said on Wednesday.

One of the sources described the attack as "state-sponsored" and several sources said that North Korea was the government involved.

The Obama administration was debating internally whether to make a public announcement of the investigators' findings, the officials said, speaking on condition of anonymity.

CNN, however, reported that an announcement pinning the blame on hackers working for Pyongyang could come as soon as Thursday.

This comes as Sony Pictures on Wednesday cancelled the Dec 25 theatrical release of its North Korea comedy "The Interview," after major US theatre chains pulled out of showing the film following threats from hackers.

Regal Cinemas and AMC Theaters were among the cinema chains announcing they will not show "The Interview" as planned on Dec 25, citing security threats by hackers that breached Sony Corp's computers.

The move is the clearest sign of the widening influence of the hackers who have also leaked Sony documents that drew global headlines, and now have forced a change of plans for a Christmas Day movie release for thousands of screens.

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

The studio said it was "deeply saddened at this brazen effort to suppress the distribution of a movie, and in the process do damage to our company."

It said it stood by the film makers of "The Interview," a comedy about two hapless journalists recruited by the CIA to assassinate North Korean leader Kim Jong Un, starring Seth Rogen and James Franco.

The movie studio is not planning to release "The Interview" through video on demand, a spokesman for the studio said on Wednesday. "Sony Pictures has no further release plans for the film," the spokesman said in response to a question about whether the movie could be released in theatres at a later date, or for home viewing through video-on-demand options.

Representatives for Rogen and Franco, who cancelled numerous scheduled appearances this week, did not respond to requests for comment.

Hackers who claimed responsibility for seizing control and leaking data from Sony's computers last month, on Tuesday warned people to stay away from cinemas showing the film, and reminded movie goers of the Sept 11, 2001 hijacked plane attacks on the United States.

The National Association of Theatre Owners, which represents movie theatres across the United States, said on Wednesday it was it was working closely with security and law enforcement agencies and that cinemas may choose not to show the film.

Several US national security officials told Reuters the government was working with entertainment companies to address the threat but had no credible evidence of a threat to moviegoers.

"The theatres are reacting out of fear and uncertainty," said Bruce Schneier, a cryptologist and one of the world's leading cybersecurity experts.

A spokesman for the Department of Homeland Security declined to comment on Wednesday, but said earlier this week there was"no credible intelligence" to substantiate the threats.

Leaks of unpublished scripts, internal emails

In addition to the threats, an early version of the script for the new James Bond film was also stolen by hackers, BBC reported.

The producers of Spectre said the screenplay was taken as part of a cyber attack on Sony Pictures Entertainment in November.

In a statement on the film's official website, Eon Productions said they were concerned the script may be published online. Spectre is due to be released in November 2015.

Sony has also seen the release of a trove of highly unflattering internal emails and other internal communications, including information about salaries, employee health records and other personal information.

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.