SEOUL, South Korea -- North Korea on Saturday proposed a joint investigation with the U.S. into the hacking attack against Sony Pictures Entertainment, warning of "serious" consequences if Washington rejects a probe that it believes would prove Pyongyang had nothing to do with the cyberattack.
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.
CBS News national security correspondent David Martin reports that, according to law enforcement sources, North Korea hacked into the Sony network by stealing the login credentials of one of the company's computer system administrators. Once logged in, the hackers wiped out hard drives, stole personal data and revealed embarrassing e-mails.
An Obama administration source told CBS News that the U.S. is reaching out to China for its cooperation in investigating the attack.
The break-in escalated to terrorist threats that caused Sony to cancel the Christmas Day release of the movie "The Interview." The comedy is 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 rumors.
"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.
On Saturday afternoon, National Security Council spokesman Mark Stroh responded by saying the U.S. stood by the FBI's conclusion.
"The government of North Korea has a long history of denying responsibility for destructive and provocative actions," Stroh said in a statement. "If the North Korean government wants to help, they can admit their culpability and compensate Sony for the damages this attack caused."
CBS News senior national security analyst Juan Zarate said on "CBS This Morning: Saturday" that North Korea's denial of any role in the attack are related to the FBI not wanting to reveal too much about what the U.S. knows about the country and how it obtained its information.
"North Korea knows that, and they know we're going to have difficulty talking publicly about the proof behind why they were behind the attack," Zarate 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, President 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," Mr. 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 theaters 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 in a technical 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 ruling regime.
Pyongyang "vehemently and categorically rejects" the resolution passed by the U.N. General Assembly that could open the door for its leaders, including Kim Jong Un, to be hauled before the International Criminal Court for crimes against humanity, according to a Foreign Ministry statement carried by KCNA.
The Security Council is due to meet Monday to discuss Pyongyang's human rights situation for the first time.
The meeting caps almost a year of international pressure, and even though ally China could use its veto power to block any action against the North, the nonbinding resolution has broad support in the General Assembly and has drawn unusually strong and vitriolic protests from Pyongyang.