Barack Obama has said US will respond "in a place and manner and time that we choose" to the hacking attack on Sony that led to the withdrawal of a satirical film about a plot to assassinate North Korea's leader Kim Jong Un.

The FBI blamed the hack on North Korea's reclusive communist government, but President Obama criticised Sony Pictures Entertainment, saying it "made a mistake" in shelving The Interview.

He told an end-of-year news conference: "I wish they (Sony executives) had spoken to me first. We cannot have a society in which some dictator some place can start imposing censorship."

Mr Obama said he imagined situations in which dictators "start seeing a documentary that they don't like or news reports that they don't like".

"Sony is a corporation. It suffered significant damage. There were threats against its employees. I am sympathetic to the concerns that they faced," Mr Obama said. "Having said all that, yes, I think they made a mistake."

The US said it detected communications between computer internet addresses known to be operated by North Korea and hacking tools left behind at the crime scene, which the FBI said contained subtle clues linking them to that country's government.

"They caused a lot of damage, and we will respond," Mr Obama said. "We will respond proportionally, and we'll respond in a place and time and manner that we choose. It's not something that I will announce here today at a press conference."

Sony has said it had had no choice but to cancel distribution of the film because cinemas were refusing to show it.

North Korea has denied that it had hacked the studio. "There is not any connection," United Nations diplomat Kim Song said.

He criticised the film but disputed his government hacked Sony and orchestrated the movie's shutdown.

"It defamed the image of our country. It made a mockery of our sovereignty. We reject it," he said. But he said there was "no relation" to the hacking.

The US decision to openly blame North Korea - which involved agreement by the State Department and intelligence agencies - escalated a world game of brinkmanship.

It happened after the disclosure of confidential Sony emails and business files and threats of terror attacks against US cinemas until Sony agreed to cancel the Christmas Day release of The Interview, which stars Seth Rogen and James Franco.

The president's pointed criticism of Sony shifted focus to whether the studio would reverse its decision, as some celebrities, including actors George Clooney and Sean Penn, have recommended.

Sony Pictures chief executive Michael Lynton said it was Mr Obama who was mistaken, noting that Sony cancelled the release only after all major cinema chains decided not to show it.

"The president, the press and the public are mistaken as to what actually happened," Mr Lynton said. "We do not own movie theatres. We cannot determine whether or not a movie will be played in movie theaters."

He did not indicate whether Sony planned to release the movie on DVD or through video-on-demand services, but the company suggested that was an option.

"The only decision that we have made with respect to release of the film was not to release it on Christmas Day in theaters, after the theatre owners declined to show it," the company said.

"After that decision, we immediately began actively surveying alternatives to enable us to release the movie on a different platform."

Mr Lynton said although YouTube distribution was "one thing that we will consider", no major video-on-demand or e-commerce site had offered to distribute the film. A DVD release falls into the same category.

Meanwhile, in a taunting new email, the hackers told Sony its executives were "very wise" to cancel the film's release and warned the studio never to release it "in any form".

In Hollywood, Clooney said the entertainment industry should push for immediate release of The Interview online. He told the trade site Deadline Sony should "do whatever you can to get this movie out. Not because everybody has to see the movie, but because I'm not going to be told we can't see the movie. That's the most important part".

And Penn said: "By caving to the outside threat, we make our nightmares real. The decision to pull The Interview is historic. It's a case of putting short-term interests ahead of the long term."

An internal FBI investigative document obtained by The Associated Press news agency identified the computers in the Sony hacking as operating in New York, Thailand, Poland, Italy, Bolivia, Singapore and Cyprus.

At least three were still functioning yesterday, responding online to internet test signals transmitted by AP. The hackers previously published some of the stolen materials with a message that included five addresses using an anonymous email service in France.

US options for acting against North Korea are limited. America already has severe trade sanctions in place and there is no appetite for military action. Even if investigators could identify and prosecute the individual hackers believed responsible, there is no guarantee that any located are overseas would ever see a US courtroom. Hacking back at North Korean targets by US government experts could encourage further attacks against American targets.

"I think the administration is going to look for other ways that we can press financial pain on the leadership of the regime and its cronies," said California congressman Adam Schiff, a member of the House of Representatives intelligence committee whose congressional district includes major film studios.

The Japanese government declined to comment on Mr Obama's statements about the importance of freedom of expression and not surrendering to threats, but said it had been working closely with the US on the hacking issue and "supports the undertaking by the US".

A Japanese analyst said blaming the cinemas was a lame excuse, but added that Sony Pictures may be worried about further releases of proprietary data that could cause far greater financial damage to the company.

"Sony Pictures is a private-sector, for-profit undertaking," said Jun Okumura, a visiting researcher at the Meiji Institute for Global Affairs in Tokyo.

"And what could Obama have offered that would have made the Sony executives change their minds? I wonder if he isn't secretly relieved that they didn't talk to him."

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