The FBI said it has enough information to conclude the North Korean government is responsible for the hacking of Sony Pictures and is "deeply concerned" by the "destructive nature" of the attack.
The agency said there is a "significant overlap" between the systems used in the Sony breach and other cyber attacks linked to North Korea, including an assault on South Korea's banks and media in 2013.
The FBI announcement came after a US official, speaking anonymously, said the probe into the hacking had also identified a possible link to China - either through host servers or use of actors.
The Chinese Embassy in Washington said China does not support "cyber illegalities" committed on its soil and called on the US to share its evidence to support the claims.
North Korea's dispute with the US over computer hacking took a new twist when the communist state lost Internet access for several hours.
A hacker group who claimed to be behind a cyber attack on Sony Pictures have posted a message online apparently mocking the FBI.
Events company Secret Cinema is planning to screen a film in protest at what they have called the 'censorship' of The Interview.