North Korea's internet went dark for several hours amid rumours 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 sole 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 that 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 Hollywood studio Sony Pictures, which was intimidated into cancelling a comedy film mocking Kim.
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 the madcap movie "The Interview."
US officials, however, called for compensation for Sony Pictures from North Korea.
"If they want to help here they could admit their culpability and compensate Sony for the damages that they caused," State Department deputy spokeswoman Marie Harf told reporters.
Dyn Research said earlier on 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.
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 favour 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.
Washington has urged Beijing - Pyongyang's closest ally - to help rein in the North's cyber hacking activities, with US Secretary of State John Kerry speaking with Chinese Foreign Minister Wang Yi 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.
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.
