The break-in resulted in the disclosure of tens of thousands 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.
"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 countermeasures while finding fault with" North Korea, the spokesman said in a statement carried by Pyongyang's official Korean Central News Agency, or KCNA.
The United States was reaching out to China, North Korea's key ally, for help as President Barack Obama weighs possible responses to the cyberattack, said a senior administration official, who wasn't authorized to comment by name and requested anonymity.
On Friday, 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.
The rivals also are locked in an international standoff over the North's nuclear and missile programs and its alleged human rights abuses.
Earlier Saturday, North Korea angrily denounced a move by the United Nations to bring its human rights record before the Security Council and renewed its threat to further bolster its nuclear deterrent against what it called a hostile policy by the U.S. to topple its regime.