US President Barack Obama on Friday warned North Korea it would face retaliation for a crippling cyber attack on Sony Pictures over an irreverent film comedy that infuriated Pyongyang.

Obama said the movie giant had "made a mistake" in canceling the Christmas Day release of "The Interview," a madcap romp about a CIA plot to kill North Korean leader Kim Jong-Un.

Sony defended its decision, made after anonymous hackers invoked the 9/11 attacks in threatening cinemas screening the film, prompting theater chains to say they would not risk showing it.

An envoy for Pyongyang denied the secretive state was behind the hacking, which led to the release of a trove of embarrassing emails, scripts and other internal communications, including information about salaries and employee health records.

Addressing reporters after the FBI said Pyongyang was to blame, Obama said Washington would never bow to "some dictator."

"We can confirm that North Korea engaged in this attack," Obama said.

"We will respond. We will respond proportionately and we'll respond in a place and time and manner that we choose."

While the president said he was sympathetic to Sony's plight, he also said: "Yes, I think they made a mistake."

"We cannot have a society in which some dictator someplace can start imposing censorship here in the United States," he added.

- 'Acts of intimidation' -

Just before Obama took the podium, the Federal Bureau of Investigation explained how it had concluded that North Korea was to blame.

The attackers used malware to break into the studio and render thousands of Sony Pictures computers inoperable, forcing the company to take its entire network offline, the FBI said.

It said analysis of the software tools used revealed links to other malware known to have been developed by "North Korean actors."

The FBI also cited "significant overlap" between the attack and other "malicious cyber-activity" with direct links to Pyongyang, including an attack on South Korean banks carried out by North Korea.

"Such acts of intimidation fall outside the bounds of acceptable state behavior," the agency said in a statement.

There was "no evidence" that North Korea had acted in concert with another country, Obama said, after reports that China -- Pyongyang's only ally -- had possibly provided assistance.

Chinese state newspaper the Global Times lashed out at "The Interview" on Saturday as "senseless cultural arrogance" in an editorial.

Senior Republican lawmaker John McCain -- the incoming chairman of the Senate Armed Services Committee -- called the cyber attack an "act of war."

And senior Democratic Senator Robert Menendez urged Secretary of State John Kerry to consider again designating Pyongyang a state sponsor of terrorism.

"This is an unacceptable act of international censorship which curtails global artistic freedom and, in aggregate, would seem to meet the definitions for acts of terrorism," Menendez wrote to Kerry.

For his part, Obama referred to it as a "crime."

Pyongyang's mission to the United Nations firmly denied any involvement.

"Our country has no relation with the hacker," North Korean political counselor Kim Song told AFP.

- 'Costs and consequences' -

Though denying involvement in the brazen November 24 cyber attack, Pyongyang has hailed it as a "righteous deed."

The North's top military body, the National Defense Commission, slammed Sony for "abetting a terrorist act while hurting the dignity of the supreme leadership," according to state news agency KCNA.

Hollywood filmmakers urged US authorities to do more to protect them against future cyber attacks, as experts estimated the attack could cost Sony Pictures hundreds of millions of dollars.

"We stand by our ('The Interview') director members Seth Rogen and Evan Goldberg and hope that a way can be found to distribute the film by some means, to demonstrate that our industry is not cowed by extremists of any type," said Directors Guild of America chief Paris Barclay.

Free speech advocates and foreign policy hawks have slammed Sony's decision to pull "The Interview" as cowardice in the face of a hidden enemy.

McCain said it set a "troubling precedent that will only empower and embolden bad actors to use cyber as an offensive weapon even more aggressively in the future."

But Sony vigorously defended the move, and said it still hoped to release "The Interview" on a different platform -- perhaps on demand or even online for free.

"We have not caved, we have not given in, we have persevered and we have not backed down," studio boss Michael Lynton told CNN.

"We have always had every desire to have the American public see this movie."

When asked how the film might be released, Lynton replied Sony was considering "a number of options" -- including putting it on YouTube for free.

Despite the controversy and the damaging hack, Lynton said he would have made the movie again, but acknowledged: "Knowing what I know now, we might have done some things slightly differently."