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N.Korea denies hacking Sony, U.S. stands by its assertion

(Adds Australian reaction)

* North Korea calls accusations "groundless slander"

* Warns of consequences if U.S. rejects proposal

* U.S. consulting Japan, China, Russia, South Korea, UK, Australia, and New Zealand on response

* Obama says Sony should not have caved in to hackers

* President chides Sony for decision to pull picture

* Studio's CEO denies it gave in to hackers

By Jack Kim and Steve Holland

SEOUL/WASHINGTON, Dec 20 (Reuters) - North Korea has said U.S. accusations that it was involved in a cyberattack on Sony Pictures were "groundless slander," and that it wanted a joint investigation into the incident with the United States.

The United States stands by its assertion that North Korea was to blame, a White House National Security Council (NSC) spokesman said on Saturday, in response to the remarks.

U.S. President Barack Obama had blamed North Korea for the devastating cyberattack on Sony, which had led to the Hollywood studio cancelling the imminent release of "The Interview," a comedy on the fictional assassination of North Korean leader Kim Jong Un.

An unnamed spokesman of North Korea's foreign ministry said there would be serious consequences if Washington refused to agree to a joint probe and continued to accuse Pyongyang, according to the North Korean U.N. mission and its official KCNA news agency.

"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," the North Korean spokesman was cited as saying by KCNA.

"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," the spokesman said.

NSC spokesman Mark Stroh dismissed this, saying: "We are confident the North Korean government is responsible for this destructive attack. We stand by this conclusion."

"The government of North Korea has a long history of denying responsibility for destructive and provocative actions," he added.

Obama said North Korea appeared to have acted alone. Washington began consultations with Japan, China, South Korea, Russia, Australia, New Zealand, and the UK seeking their assistance in reining in North Korea.

Japan and South Korea said they would cooperate. China, North Korea's only major ally, has yet to respond, but a Beijing-run newspaper said "The Interview" was not a movie for Hollywood or U.S. society to be proud of.

An Obama administration official said on Saturday: "In our cybersecurity discussions, both China and the United States have expressed the view that conducting destructive attacks in cyberspace is outside the norms of appropriate cyber behavior."