North Korea's Internet went dark for several hours amid rumors of US retaliation over its alleged hacking of a Hollywood studio, just as the pariah state came under attack at the UN over its rights record.

It was not clear who or what had shut down Pyongyang's web connections, but cyber experts said the country's already limited Internet went completely offline overnight from Monday to Tuesday local time.

Piling further pressure on Kim Jong-Un's regime, UN members debated North Korea's brutal treatment of its huge prison population after China, its only major ally, was rebuffed in a bid to shelve the issue.

US-based Internet analysts Dyn Research said Pyongyang's four online networks, all connected through Chinese telecom provider China Unicom, had been offline for nine hours and 31 minutes before services resumed on Tuesday morning.

Dyn Research said Pyongyang's very limited infrastructure could be vulnerable to power outages but the way it had collapsed "seems consistent with a fragile network under external attack".

US President Barack Obama and the FBI have accused North Korea of being behind the hacking of Sony Pictures, which decided to cancel the Christmas Day release of comedy film "The Interview".

Washington officials refused to comment on speculation that the North Korean Internet blackout was the first stage in what Obama has warned will be a "proportionate response" to the hack.

North Korea has angrily insisted that it had nothing to do with the theft and leaking of Sony company secrets nor threats against moviegoers, but it has also condemned Sony's madcap movie, which features a fictional plot to kill Kim.

Pyongyang has also vowed reprisals if the US brings in new sanctions such as restoring the country to a list of state sponsors of terrorism.

China on Tuesday suggested Washington and Pyongyang hold talks over cyber hacking. US officials, however, have dismissed a North Korean proposal for a joint investigation into the Sony hack and instead called for the hermit state to compensate the film studio.

Dyn Research said earlier Monday that Internet connectivity between North Korea and the outside world, never good at the best of times, had begun to show signs of instability over the weekend.

"This is different from short duration outages we have seen in the past," Earl Zmijewski, vice president of data analytics at Dyn, told AFP.

- 'Living nightmare' of repression -

But Zmijewski stressed it was impossible to say what had caused the outage. "They could have elected to simply pull the plug or they could have suffered from some sort of failure or attack," he said.

The diplomatic row comes as China failed on Monday to block the first-ever UN Security Council meeting on North Korea's dismal rights record after a strong majority of members voted in favor of it.

US ambassador Samantha Power -- backed by envoys from Britain, Australia and France -- said North Korean citizens experience a "living nightmare" of political repression.

She recalled testimony from a starving prison camp survivor who picked kernels of corn from cattle dung to eat and of a former guard who said prison wardens routinely raped prisoners.

Power dismissed Pyongyang's offer of a joint investigation into the hack as "absurd," urging the council to take action against North Korean leaders.

No decision was taken on Monday on a call to refer North Korea to the International Criminal Court for crimes against humanity, but campaigners urged the body to keep the issue alive.

Beijing -- which has itself been accused by Washington of extensive hacking of civilian and government networks -- meanwhile suggested on Tuesday that "the US and the DPRK can have communication" on cyber hacking, using North Korea's official title.

Washington has urged Beijing, Pyongyang's closest ally, to help rein in the North's cyber crime activities, with US Secretary of State John Kerry speaking with his Chinese counterpart over the weekend to discuss the problem.

China's foreign ministry on Monday condemned "cyber terrorism" in any form but did not refer directly to North Korea.

Elsewhere, Seoul heightened its readiness against cyber attacks from North Korean and other hackers after a series of online information leaks about the country's nuclear power plants.

North Korea has limited access to the worldwide web with just four networks on the global Internet, compared to 150,000 in the United States, analysts say.

Pyongyang's main Internet presence is through its Uriminzokkiri website, which has Twitter and Flickr feeds and is best known for posting propaganda videos excoriating South Korea and the United States.