The proposal was seen by analysts as a typical ploy by the North to try to show that it is sincere, even though it knows the U.S. would never accept its offer for a joint investigation.
U.S. officials blame North Korea for the hacking, 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 tens of thousands of confidential Sony emails and business files, and escalated to threats of terror attacks against U.S. movie theatres 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, an unidentified 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. He also said Washington was slandering Pyongyang by spreading unfounded rumours.
"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.
"We have a way to prove that we have nothing to do with the case without resorting to torture, as the CIA does," he said, adding that the U.S. lacks any specific evidence tying North Korea to the hacking.
In Washington, a spokesman for the White House National Security Council, Mark Stroh, said the U.S. stands by the FBI's conclusion that "the North Korean government is responsible for this destructive attack."
"The government of North Korea has a long history of denying responsibility for destructive and provocative actions," Stroh said. "If the North Korean government wants to help, they can admit their culpability and compensate Sony for the damages this attack caused."
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. Although China holds considerable leverage over the North and its technological infrastructure, involving Beijing could pose complications because Obama has pointedly accused China of engaging in its own acts of cybertheft.
An editorial in the Global Times, a newspaper published by China's ruling Communist Party, said that any civilized country will oppose hacker attacks or terror threats, but it also condemned the movie. "The vicious mocking of Kim is only a result of senseless cultural arrogance," it said.
Koh Yu-hwan, a professor at Seoul's Dongguk University, called the North's proposal a "typical" tactic the country has taken in similar disputes with rival countries. In 2010, North Korea proposed a joint investigation after a South Korean-led international team concluded that the North was behind a torpedo attack that killed 46 South Korean sailors, though Pyongyang denied its involvement. South Korea rejected the North's offer for the joint probe.
"They are now talking about a joint investigation because they think there is no conclusive evidence," Koh said. "But the U.S. won't accede to a joint investigation for the crime."
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.
"I wish they had spoken to me first. ... We cannot have a society in which some dictator someplace can start imposing censorship," Obama said at a year-end news conference, speaking of executives at Sony Pictures Entertainment.
Sony said it had had no choice but to cancel distribution of the movie because theatres were refusing to show it.
U.S. options for acting against North Korea are limited. The U.S. already has severe trade sanctions in place, and there is no appetite for military action. Even if investigators could identify and prosecute the individual hackers believed responsible, there's no guarantee that any located are overseas would ever see a U.S. courtroom. Hacking back at North Korean targets by U.S. government experts could encourage further attacks against American targets.
North Korea and the U.S. remain technically in a state of war because the 1950-53 Korean War ended with an armistice, not a peace treaty. 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.
Associated Press writer Eric Talmadge in Tokyo contributed to this report.
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