North Korea's limited internet service collapsed for more than nine hours just days after the US vowed to retaliate for a cyber-attack on Sony, which has been blamed on the reclusive state.
A US-based analyst said all internet went down after a period of instability over the weekend before links were eventually restored.
"For the past 24 hours North Korea's connectivity to the outside world has been progressively getting degraded to the point now that they are totally offline," said Doug Madory, director of internet analysis at Dyn Research.
"There's either a benign explanation - their routers are perhaps having a software glitch; that's possible. It also seems possible that somebody can be directing some sort of an attack against them and they're having trouble staying online."
Sony pulled The Interview - a comedy about the assassination of North Korea's leader Kim Jong-Un - after hackers threatened showings of the movie.
The group, calling itself Guardians of Peace, had already leaked five unreleased films, the script of the next James Bond movie, embarrassing email exchanges between executives and private individuals' data after attacking Sony's systems.
Pyongyang has repeatedly denied any role in the attack but said it could have been carried out by the country's supporters.
But the FBI blamed North Korea for the devastating attack on the media giant and President Barack Obama said the US would respond "in a place and time and manner that we choose".
State Department spokeswoman Marie Harf said she could not confirm North Korea had been the target of a cyber-attack.
"We aren't going to discuss...publicly, operational details about the possible response options or comment on those kind of reports in anyway except to say that as we implement our responses, some will be seen, some may not be seen," she said.
However, Ms Harf did respond to Pyongyang's calls for a joint investigation into the attack, saying: "If they want to help here they could admit their culpability and compensate Sony for the damages that they caused."
The internet is only available to trusted government officials in North Korea and its main web presence is through its Uriminzokkiri website, which has Twitter and Flickr feeds best known for sharing propaganda videos attacking the US and South Korea.
Mr Madory said the internet connection has historically been stable, although it has come under attack in the past. He added that it would not need to be "some big nation state" to cause such a shutdown.
The internet problems came as the US called North Korea a "living nightmare" at the first-ever UN Security Council meeting on its human rights record.
The talks at the 15-member council opened after China, Pyongyang's ally, failed to block the meeting.
Pyongyang had earlier branded the US "an ill-famed cesspool of injustice and terrorism" and praised the "surprisingly sophisticated, destructive and threatening cyber warfare" against Sony.
