North Korea's internet is thought to be completely down after days of connectivity problems, Digital Spy said.

The U.S. – which accused the country of being behind the recent Sony hacking – has refused to comment on the outage.

While the White House has refused to comment, the U.S. Department of State said it would not publicly discuss the "operational details" of its response to the recent cyber threats.

Spokeswoman Marie Harf said: "We aren't going to discuss, you know, publicly operational details about the possible response options or comment on those kind of reports in any way except to say that as we implement our responses, some will be seen, some may not be seen."

Last week, North Korea denied any involvement with the Sony hacking and offered to hold a joint investigation with the U.S. over it.

The hackers – who refer to themselves as the Guardians of Peace – referenced the 9/11 attacks in their warning against the release of The Interview this week.

The threats resulted in the cancellation of the film's theatrical release, but Sony has since hinted that the film may be distributed another way.