North Korea says it can prove it had nothing to do with the cyber-attack on Sony and proposes a joint investigation with the US.

The North Korean news agency KCNA warned there would be "grave consequences" if the US refuses to take up the offer.

State media called a claim by the FBI that North Korea was behind the attack on the entertainment giant a "slander".

The North's foreign minister, quoted by KCNA, said: "As the United States is spreading groundless allegations and slandering us, we propose a joint investigation with it into this incident."

"Without resorting to such tortures as were used by the US CIA, we have means to prove that this incident has nothing to do with us."

Sony meanwhile has defended its decision to cancel the film mocking the North Korean regime after the studio suffered the damaging cyber-attack.

In a statement, the company said it had "no choice" but to pull The Interview, because cinema chains across the US had backed away from showing the film, which depicts a plot to assassinate North Korean leader Kim Jong-Un.

The decision was made after the group claiming responsibility for the cyber-attack made terrorist threats against US cinemas if they showed the movie, which stars Seth Rogen and James Franco.

President Barack Obama strongly criticised the move, saying he believed the studio had "made a mistake".

Celebrities and film-makers have also slammed the decision, which was made earlier this week. Mr Obama said: "I wish they had spoken to me first."

"We cannot have a society in which some dictatorship someplace can start imposing censorship."

"Without theaters, we could not release it in the theaters on Christmas Day," Sony said in response.

"We had no choice."

It insists it has only cancelled the Christmas Day release and it has been "actively surveying alternatives" to release the film on another platform.

"It is still our hope that anyone who wants to see this movie will get the opportunity to do so," Sony said.

Sony's chief executive, Michael Lynton, has also defended the company's actions, telling CNN: "We experienced the worst cyber-attack in American history."

"We have not caved, we have not given in, we have persevered and we have not backed down. We have always had every desire to have the American public see this movie."

Mr Lynton said President Obama, the media and the public "are mistaken as to what actually happened" and added he had personally talked to senior advisers at the White House, who were "certainly aware of the situation".

The FBI revealed on Friday it believed North Korea was behind the cyber-attack on Sony, something Pyongyang has denied.

However, a North Korean diplomat did say the film "defamed the image of our country". The FBI called the attack, which led to a series of embarrassing leaks, an unacceptable act of state-sponsored "intimidation".

The agency said technical analysis of malware used in the attack found links to malware that "North Korean actors" had developed and found a "significant overlap" with "other malicious cyber activity" previously tied to Pyongyang.

The group claiming responsibility for the attack, who call themselves Guardians of Peace, praised the decision to cancel the film's release in a statement provided to CNN on Friday.

Originally posted at 10.43am