Internet connections between North Korea and the rest of the world are suffering some of their worst ever outages just days after US President Barack Obama warned of a "proportional response" to the Sony hacking.
Very few people in the country have access to the internet, with connections often failing.
However, the continuous problems reportedly being experienced have led experts to raise the possibility that it might be under a cyber-attack.
Doug Madory, director of Internet analysis at Dyn Research, said the internet connectivity problems were discovered in the last 24 hours and have become progressively worse to the point that "North Korea's totally down".
"I haven't seen such a steady beat of routing instability and outages in KP before," he told North Korea Tech.
"Usually there are isolated blips, not continuous connectivity problems. I wouldn't be surprised if they are absorbing some sort of attack presently."
Although very few citizens have access to the internet, it allows the country's state media to link to the outside world.
The outage comes just days after Mr Obama pledged to consider officially labelling North Korea, accused by Washington of hacking Sony Pictures, a state sponsor of terrorism.
The communist state's internet access is wired through China, which today, in a foreign ministry statement, said it "opposes cyber-attacks and cyber-terrorism in all of its forms", without referring directly to its ally North Korea.
Workers remove a poster for the film
a day after Sony cancelled its release following the hack. Photo / AP
It was not immediately clear if the connectivity problems were an act of retribution for the hack, that the FBI last week linked to North Korea.
Washington has accused Pyongyang of being behind the hack that led to the release of embarrassing company emails and caused Sony executives to halt the debut of the comedy action film The Interview.
The film about a fictional CIA plot to kill the country's leader infuriated North Korea, although Pyongyang has repeatedly denied it was behind the cyber assault.
Obama: 'An act of cyber-vandalism'
Despite calls from Republican critics for a robust response to the alleged hack, Mr Obama told CNN in an interview: "I don't think it was an act of war. I think it was an act of cyber-vandalism that was very costly, very expensive. We take it very seriously."
He also promised to "review" whether to return North Korea to the US list of state sponsors of terrorism, but added: "We've got very clear criteria as to what it means for a state to sponsor terrorism. And we don't make those judgments just based on the news of the day."
The White House declined to comment today. State Department spokeswoman Marie Harf told reporters that of the federal government responses, "some will be seen, some may not be seen".
US President Barack Obama says he takes the Sony hack "very seriously". Photo / AP
North Korea has threatened to hit back at the White House and other US targets if it was sanctioned over the alleged hacking.
Its National Defense Commission, in a statement on the official news agency, said the North Korean army and people "are fully ready to stand in confrontation with the US in all war spaces including cyber-warfare space to blow up those citadels".
According to the FBI, there is "significant overlap" between the Sony Pictures attack and other "malicious cyber-activity" with direct links to Pyongyang, including an attack last year on South Korean banks blamed on the North.
The South's Korea Hydro and Nuclear Power Co (KHNP) also began conducting drills at its four nuclear plant complexes today after a series of online information leaks by a suspected hacker.
The hacker, using an account entitled "president of the anti-nuclear reactor group", published a variety of information on Twitter, including designs and manuals for two reactors as well as personal information on some 10,000 KHNP employees.
There did not appear to be any link between the drill and the Sony Pictures hack, and North Korea says it has never attempted or made a cyber attack on South Korea.
US urges North Korea to admit attack
The United States urged North Korea yesterday to admit it ordered the Sony cyber-attack and to pay for the damage it had caused.
"If they want to help here they could admit their culpability and compensate Sony for the damages that they caused," deputy State Department spokeswoman Marie Harf told reporters.
Washington is "confident the North Korean government is responsible for this destructive attack," Ms Harf insisted.
The government of the hermit state also has a "long history of denying responsibility" for provocative actions, she added.
Asked about threats from Pyongyang to hit back if it is sanctioned over the Sony affair, Ms Harf said: "We do urge North Korea to exercise restraint, to refrain from further threatening actions at this time."
Ms Harf said she could not comment on online reports that alleged North Korea's limited internet connectivity had been sharply curtailed Monday, suggesting it was under attack.
The US administration is "discussing a range of options" in response to the Sony hacking, she said, stressing however that Washington would not outline publicly what moves it planned to take.
"As we implement our responses, some will be seen, some may not be seen," she said.
- Daily Mail, AFP