A cyber attack on Sony Pictures that forced the cancellation of a major film release is being seen as a serious national security matter, the US 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 withdrew The Interview, a new comedy film about North Korea's leader, 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 11 September 2001 terror attacks, they said "the world will be full of fear" if the film was screened.

Team America 'pulled'
Three cinemas said replacement screenings of Team America, a film which ridicules the former North Korean leader Kim Jong-il, had also been cancelled.

The Plaza Atlanta and Ohio's Capitol Theatre both tweeted their screenings had been cancelled by the film's makers Paramount Pictures, while the Alamo Drafthouse said the film had been "removed from release". Paramount has declined to comment.

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

At a White House briefing on Thursday, 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.

Source: http://www.bbc.co.uk/news/world-us-canada-30538154