North Korean officials said Saturday that the country had nothing to do with the attack against Sony Pictures Entertainment, Reuters reported, adding that the country has called for a joint investigation with the U.S. into the hack.

The attack against Sony Pictures has led to the cancellation of the Christmas release of “The Interview”, with hackers calling the Sony decision a “wise” one. The FBI said that it had “enough information” to prove North Korea’s involvement in the hack, but Pyongyang stood by its claims that it had nothing to do with it. North Korean officials also said that there will be “grave consequences” if U.S. chooses not to co-operate in the joint investigation.

The FBI had said that its officials had found a malware that "revealed links to other malware that the FBI knows North Korean actors previously developed." FBI also said, according to Fox News, that it noticed a “significant overlap between the infrastructure used in this attack and other malicious cyber activity the U.S. government has previously linked directly to North Korea."

Meanwhile, the hacking group, known as the Guardians of Peace, sent an email to Sony officials saying that they will “ensure the security of your data unless you make additional trouble.” The group also asked Sony Pictures to never release the film amid the company's search for alternative ways to release the film.

"It's very wise that you have made the decision to cancel the release of The Interview. It will be very useful for you," the group reportedly said, in the email, adding: "Now we want you never let the movie released, distributed or leaked in any form of, for instance, DVD or piracy.”

U.S. President Barack Obama said Friday that complying with such anonymous threats would only encourage attackers.

"I am sympathetic to the concerns that they face. Having said all that, yes I think they made a mistake," Obama said, at a press conference, adding: “We cannot have a society where some dictator someplace can impose censorship here in the U.S.”