(AP) -- President Barack Obama said Friday that Sony Pictures Entertainment "made a mistake" in shelving a satirical film about a plot to assassinate North Korea's leader. He declared the United States would respond "in a place and manner and time that we choose" to a hack attack on Sony that the FBI blamed on the communist government.

Speaking of Sony executives, Obama said at a year-end news conference, "I wish they had spoken to me first. ... We cannot have a society in which some dictatorship someplace can start imposing censorship."

Obama said he imagined situations in which dictators "start seeing a documentary that they don't like or news reports that they don't like."

The president spoke not long after the FBI accused the North Korean government of being responsible for the hacking attack against Sony, providing the most detailed accounting to date of the expensive break-in. Obama's pointed criticism of Sony shifted focus to whether the studio would reverse its decision, as some leading celebrities -- including actor George Clooney and comedian Patton Oswalt -- have recommended.

"Sony is a corporation. It suffered significant damage. There were threats against its employees. I am sympathetic to the concerns that they faced," he said. "Having said all that, yes, I think they made a mistake."

The administration earlier in the day formally accused North Korea's government of being responsible but offered few hints about how it might retaliate. Its evidence: The U.S. detected communications between computer Internet addresses known to be operated by North Korea and hacking tools left behind at the crime scene, which the FBI said contained subtle clues linking them to that country's government.

The decision to openly blame North Korea -- which involved the State Department and U.S. intelligence agencies -- escalated an intriguing global game of brinkmanship. It included the disclosure of confidential Sony emails and business files and threats of terror attacks against U.S. movie theaters until Sony agreed to cancel the Christmas Day release of its comedy, "The Interview." The hackers had demanded that withdrawal partly over a scene depicting the assassination of North Korea's leader.

"The FBI now has enough information to conclude that the North Korean government is responsible for these actions," said the U.S. statement, which was not attributed to any official by name. It added: "North Korea's actions were intended to inflict significant harm on a U.S. business and suppress the right of American citizens to express themselves."

The statement included a general promise to impose "costs and consequences" on any person, group or government using cyberattacks to threaten the U.S. or its interests. Obama wasn't any more specific.

"They caused a lot of damage, and we will respond," Obama said. "We will respond proportionally, and we'll respond in a place and time and manner that we choose. It's not something that I will announce here today at a press conference."

North Korea has denied it was involved but praised the hacking as a "righteous deed." On Friday, a North Korean diplomat to the United Nations, Kim Un Chol, declined to comment on the American accusations.

In a taunting new email the hackers sent to Sony, they told the Hollywood studio that executives were "very wise" to cancel the movie's release and said they planned no further disclosures of Sony's confidential materials "as long as you make no more trouble." The message warned Sony never to release the film "in any form," including on DVD. The email was sent to several employees. It was confirmed Friday by a person close to the studio who requested anonymity because the person wasn't authorized to speak publicly about the matter.

In Hollywood, Clooney said the entertainment industry should push for immediate release of "The Interview" online. In an interview with the trade site Deadline, Clooney urged Sony to "do whatever you can to get this movie out. Not because everybody has to see the movie, but because I'm not going to be told we can't see the movie. That's the most important part."

Oswalt wrote on Twitter, "We just gave a comfy foothold to censorship (and) it doesn't get any better from this point on."

The evidence implicating North Korea previously was described as largely circumstantial, including unspecified clues in the hacking tools left behind and the involvement of at least one computer in Bolivia previously traced to other attacks blamed on North Korea. Now, the FBI said, clues included similarities to other tools developed by North Korea in specific lines of computer code, encryption algorithms and data deletion methods. More significantly, the FBI discovered that computer Internet addresses known to be operated by North Korea were communicating directly with other computers used to deploy and control the hacking tools and collect the stolen Sony files.

The FBI noted in its statement that it worked closely on the investigation with "other U.S. government departments and agencies." Those included the National Security Agency, a person familiar with the case said on condition of anonymity because some information NSA was providing in the case was highly classified.

An internal FBI investigative document obtained by The Associated Press identified the computers in the Sony hacking as operating in New York, Thailand, Poland, Italy, Bolivia, Singapore and Cyprus. At least three were still functioning Friday, responding online to Internet test signals transmitted by the AP. The hackers previously published some of the stolen materials with a message that included five addresses using an anonymous email service in France.

U.S. options for acting against North Korea are limited. The U.S. already has severe trade sanctions in place, and there is no appetite for military action. Even if investigators could identify and prosecute the individual hackers believed responsible, there's no guarantee that any located are overseas would ever see a U.S. courtroom. Hacking back at North Korean targets by U.S. government experts could encourage further attacks against American targets.

Evans Revere, a former State Department official and specialist on Korea, said if U.S. officials connect North Korea not only to the hacking attack but to the threats to carry out 9/11-style attacks against movie theaters, a case could be made to put North Korea again on a list of state sponsors of terrorism. That designation now is held by Iran, Sudan, Syria and Cuba. North Korea was on the list for 20 years until it was taken off in 2008 by the Bush administration during nuclear negotiations..

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Associated Press Writers Jake Coyle in New York and Cara Anna at the United Nations contributed to this report.