North Korea is the prime suspect in the hacking of Sony Pictures' networks last month, a U.S. investigation has concluded.
The Federal Bureau of Investigation said on Friday, shortly before the president's end-of-year address, that it had "enough information to conclude" the rogue state is responsible for the attack.
Technical analysis carried out by the agency showed evidence of North Korea's involvement.
"The FBI also observed 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," an FBI statement read.
The tools used in the Sony attack have "similarities" to a cyberattack carried out on South Korean banks and media outlets, which "were carried out" by the North Koreans, the statement read.
President Obama has been weighing retaliatory responses that will be "proportional, but not necessarily noticeable," sister site CBS News' Major Garrett reported on Friday.
Although it's not clear what those sanctions may be, CNBC suggested that companies working within North Korea may face financial sanctions.
An earlier Reuters report citing an unnamed official, who spoke on the condition of anonymity, said there were links to China, either through collaboration with Chinese hackers or by using servers hosted on its territory.
The FBI did not say whether any other actor or state was involved in the attack.
President Obama said later at his end-of-year speech that there was "no indication" North Korea worked with anyone else in the cyberattack.
The cyberattack, which left Sony's systems crippled and terabytes of data leaked online -- including email inboxes and confidential memos -- was considered a "serious national security matter" by the Obama administration on Thursday.
Sony was attacked in November by hackers claiming to protest the release of a film, "The Interview," starring Seth Rogan and James Franco, that tells a fictional story about two journalists who are recruited by a U.S. spy agency to assassinate Kim Jong Un, the leader of North Korea.
The hacker group, calling itself The Guardians of Peace, claimed responsibility for the attack.
North Korea denied any involvement in attack.
Later correspondence from the alleged hackers implied September 11-style attacks on those who saw the film. This led Sony to cancel showings and screenings of the film, effectively withdrawing it from the market.
Sony is said to have lost tens of millions in revenue after pulling the movie.
Updated at 2:20pm ET: with comments from President Obama during his end-of-year speech.