North Korea called accusations it was responsible for the widely reported cyberattack on the Sony Pictures Entertainment unit of the Sony Corp. “groundless slander” in its response Saturday to a report by U.S. investigators. The country also called for a joint investigation of the incident, Reuters reported. Pyongyang indicated there would be “grave consequences” if Washington refused to agree to the probe, the state-run KCNA news agency said.

“We propose to conduct a joint investigation with the U.S. in response to groundless slander being perpetrated by the U.S. by mobilizing public opinion,” a representative of North Korea’s foreign ministry said. “If the U.S. refuses to accept our proposal for a joint investigation and continues to talk about some kind of response by dragging us into the case, it must remember there will be grave consequences.”

Earlier, Kim Song, a North Korean diplomat at the United Nations, denied the allegation that his country was involved in the hack, telling the Associated Press Friday: “There is not any connection. ... It defamed the image of our country. It made a mockery of our sovereignty. We reject it. But there is no relation” to the hacking. He criticized the film associated with the cyberattack, “The Interview,” but said his government had neither hacked Sony nor orchestrated the movie’s shuttering.

U.S. President Barack Obama said Friday that North Korea was responsible for the cyberattack that led the Hollywood studio to canceling the release of the film, a comedy about the fictional assassination of North Korean leader Kim Jong Un. The hack resulted in the release of personal information about thousands of people and posted a number of Sony movies online that have yet to make their official debuts. The FBI said Pyongyang’s actions fell “outside the bounds of acceptable state behavior.”

Obama said it appeared North Korea had acted alone and that the U.S. has begun consultations with Japan, China, South Korea and Russia to seek their assistance in reining in the isolated North Korea.