SEOUL, South Korea (AP) — North Korea has proposed a joint investigation with the U.S. into the hacking attack against Sony Pictures Entertainment.

U.S. officials blame North Korea for the hacking, citing the tools used in the Sony attack and previous hacks linked to the North.

The break-in resulted in the disclosure of tens of thousands of confidential Sony emails and business files, and escalated to terrorist threats that caused Sony to cancel the release of the movie "The Interview." The comedy is about a plot to assassinate North Korean leader Kim Jong Un.

An unidentified Foreign Ministry spokesman in Pyongyang said Saturday that the U.S. would face unspecified "grave consequences" if it rejects its proposal for the joint investigation.

He also said North Korea knows how to prove it's not responsible for the hacking.

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