The Obama administration on Friday formally accused the North Korean government of being responsible for the devastating hacking attack against Sony Pictures Entertainment, providing the most detailed accounting to date of a hugely expensive break-in that could lead to a U.S. response.

The FBI said in a statement it has enough evidence to conclude that North Korea was behind the punishing breach, which resulted in the disclosure of tens of thousands of leaked emails and other materials.

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

The FBI's case cited, among other factors, technical similarities between the Sony break-in and past "malicious cyber activity" linked directly to North Korea.

Obama administration officials had previously declined to openly blame North Korea but said they were weighing various options for a response. The statement Friday did not reveal what options were being considered. President Barack Obama is expected to face questions about the Sony hack at a year-end news conference with reporters later Friday.

The break-in escalated to terrorist threats that promoted Sony to cancel the Christmas release of the movie "The Interview." The comedy is about a plot to assassinate North Korea's leader, Kim Jong Un.

Meanwhile, the cyber-terrorists behind the attack sent a message to studio execs late Thursday giving them kudos for the "very wise" decision to not release the "The Interview" in any format, according to a report.

"Now we want you never let the movie released, distributed or leaked in any form of, for instance, DVD or piracy," the hackers said in a message sent to Sony brass, CNN reported.

The missive also implied that additional data leaks would stop now that Sony has dropped plans to distribute the film, which was originally slated for a Dec. 25 theatrical debut.

The FBI probe into the hack found North Korea was involved and that there may also be a Chinese link, either through collaboration with Chinese actors or the use of Chinese servers to mask the origin of the attack, a U.S. official said.

The White House has called the strike against the big Hollywood studio a matter of national security and said it was weighing a "proportional response."

North Korea has previously denied involvement, and a North Korean U.N. diplomat on Thursday declined to comment on the accusation that Pyongyang was responsible.

The attack on Sony, more than three weeks ago, is the most destructive hacking of a company on U.S. soil, conducted by hackers calling themselves "Guardians of Peace."

It brought down the computer network at Sony Pictures Entertainment, prompted the leak of embarrassing emails, and led to Sony's cancellation of "The Interview," a comic film that culminates in a scene depicting the assassination of North Korean leader Kim Jong Un.

U.S. movie theaters had said they would not show the film after hackers made threats against cinemas and audiences. Many in Hollywood and Washington criticized Sony's cancellation as caving in to the hackers.

Sony Pictures is a unit of Sony Corp.

U.S. experts say options for the Obama administration could include cyber retaliation, financial sanctions and even a boost in U.S. military support to South Korea to send a stern message to North Korea.

Another could be to return North Korea to a U.S. list of State Sponsors of Terrorism from which it was removed in 2008, but the effect of any response could be limited given North Korea's isolation and the fact that it is already heavily sanctioned.

Obama's national security team has struggled to come up with a response tough enough to get its message across but not so extreme as to provoke North Korea to engage in further cyber warfare.

A dilemma for the administration was how much of its evidence it could make public without divulging the technological means it has to trace cyber attacks back to the source.