BEIJING - Denying U.S. allegations that it was behind a cyberattack on Sony Pictures as an "unfounded rumor," North Korea on Saturday proposed a "joint investigation" into the hacking that prompted the studio to cancel the theatrical release of the comedy

The Interview

, which centers on a plot to assassinate North Korean leader Kim Jong Un.

"We have a way to prove that we have nothing to do with the case," North Korea said in a statement carried by the official Korean Central News Agency, quoting an unidentified spokesman from the North Korean Foreign Ministry. Pyongyang warned that the "U.S. should bear in mind that it will face serious consequences in case it rejects our proposal for joint investigation and presses for what it called countermeasure(s)."

The FBI on Friday blamed North Korea for the cyberattack on the studio, which divulged executives' salaries, sensitive e-mails and scripts. The attackers took and released full-length films including Annie and Fury.

The Pyongyang government said American officials had leveled the accusations "without presenting any specific evidence."

"Clear evidence is needed to charge a sovereign state with a crime," the statement said.

The U.S. had no immediate response to the proposal, and it seemed highly unlikely that Washington would accept the offer.

President Obama on Friday said the U.S. would respond to the cyberattack, though he declined to outline the options under consideration. "They caused a lot of damage. And we will respond," he said. "We will respond proportionally, and we'll respond in a place and time and manner that we choose."

The FBI said technical analysis of the data-deletion malware in the Sony hack "links to other malware that the FBI knows North Korean actors previously deployed." Agents found similarities in specific lines of code, encryption algorithms, data-deletion methods, and compromised networks.

The bureau also said it found overlap in the system used in the Sony attack and "other malicious cyberactivity the U.S. government has previously linked directly to North Korea."