North Korea on Saturday proposed a joint investigation with the U.S. into the hacking attack against Sony Pictures Entertainment, warning of consequences if Washington rejects the probe. The FBI blamed North Korea for the hacking of SPE's servers, citing the tools used in the Sony attack and previous hacks linked to the North, and have vowed to respond. The break-in resulted in the disclosure of confidential Sony emails and business files, and escalated to threats of terror attacks against U.S. movie theaters that caused Sony to cancel the Christmas Day release of "The Interview," a comedy about a plot to assassinate North Korean leader Kim Jong Un.

On Saturday, a North Korean Foreign Ministry spokesman in Pyongyang proposed the joint investigation with the U.S., saying the North knows how to prove it's not responsible for the hacking and that the U.S.l have been unfounded rumors.

"We propose the U.S. side conducting a joint investigation into the case, given that Washington is slandering Pyongyang by spreading unfounded rumor. We have a way to prove that we have nothing to do with the case without resorting to torture as what the CIA does," the spokesman said in a statement carried by Pyongyang's official Korean Central News Agency, or KCNA.

"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 while finding fault with the DPRK," the statement continued.

On Friday, President Barack Obama declared that Sony "made a mistake" in shelving the satirical film about a plot to assassinate the North Korean leader, and pledged that the U.S. would respond "in a place and manner and time that we choose" to the hacking attack on Sony that led to the movie's withdrawal.