The cyber attack on Sony Pictures Entertainment that forced the cancellation of The Interview movie release is being seen as a serious national security matter, the White House says.

A White House spokesman said the US believed the hacking was the work of a “sophisticated actor” – but refused to confirm if North Korea was responsible.

Sony Pictures withdrew The Interview, a new comedy film about North Korean leader Kim Jong-un, after threats from hackers.

Hackers have already released sensitive information stored on Sony computers.

They later issued a warning to members of the public planning to see The Interview.

Referring to the 9/11 terror attacks, they said “the world will be full of fear” if the film was screened.

Many cinemas scrapped plans to show the film, and Sony then cancelled the release of the film altogether – moves criticized in Hollywood as an attack on the freedom of expression.

At a White House briefing on December 18, spokesman Josh Earnest said US officials had held daily discussions about the Sony cyber attack and were considering an “appropriate response”.

However, he refused to comment on who was responsible, saying he did not wish to pre-empt an investigation by the Department of Justice and the FBI.

The Interview, made by Sony Pictures, features James Franco and Seth Rogen as two journalists who are granted an audience with Kim Jong-un.

The CIA then enlists the pair to assassinate him.

The Interview was due to have been released over Christmas.

In November, a cyber attack crippled computers at Sony and led to upcoming films and workers’ personal data being leaked online.

The hackers also released salary details and social security numbers for thousands of Sony employees – including celebrities.

Earlier this month, North Korea denied hacking into Sony’s computers – but praised the attack itself as a “righteous deed”.

An article on North Korea’s state-run KCNA news agency, quoting the country’s top military body, said suggestions that Pyongyang was behind the attack were “wild rumor”.

However, it warned the US that “there are a great number of supporters and sympathizers” of North Korea “all over the world” who may have carried out the attack.

In the article, Sony Pictures was accused of “abetting a terrorist act” and “hurting the dignity of the supreme leadership” of North Korea by producing the movie.

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