China is North Korea's only major ally, and would be central to any US efforts to crack down on the isolated state. But the United States has also accused China of cyber spying in the past and a US official has said the attack on Sony could have used Chinese servers to mask its origin.
President Barack Obama said Friday the US would respond to the cyberattack, though he did not say how, after the FBI publicly blamed North Korea.
An unnamed spokesman of the North's foreign ministry said there would be "grave consequences" if Washington refused to agree to the joint probe and continued to accuse the North, the official KCNA news agency reported.
US experts say Obama's options could include cyber retaliation, financial sanctions, criminal indictments against individuals implicated in the attack or even a boost in US military support to South Korea.
While US officials are saying privately that they believe North Korea was connected to the attack, the White House has not said so publicly.
Russia is also one of five countries involved in talks with North Korea on its nuclear programme. The others are South Korea, China, the United States and Japan.
North Korea routinely threatens to destroy its neighbour, though it has recently proposed steps to ease tension
North Korea's Kim Jong-un has warned the reclusive communist country could become "a bargaining chip for the strong."
North Korea on Saturday rejected the findings of a UN panel, which accused the state of crimes against humanity that evoked Nazi-era atrocities, saying they were based on "lies and fabrications deliberately cooked up by hostile forces and riff-raffs."
North Korea stepped up its bellicose rhetoric on Tuesday threatening to go beyond carrying out a promised third nuclear test in response to what it believes are "hostile" sanctions imposed after a December rocket launch.