North Korea's Internet connection with the world has been hit by a series of outages in the last 24 hours, according to a researcher.

Problems began on Monday morning, local time in Korea, when the handful of websites hosted on servers in Pyongyang became unresponsive. Over several hours, connectivity was spotty with connections sometimes succeeding but sometimes not.

"I haven't seen such a steady beat of routing instability and outages in [North Korean Internet space] before," said Doug Madory, director of Internet analysis at Dyn Research. "Usually there are isolated blips, not continuous connectivity problems. I wouldn't be surprised if they are absorbing some sort of attack presently."

The news has led to speculation that it might be the result of a promised but unspecified response by the U.S. to an attack against Sony Pictures, but it's impossible to determine the cause from the network problems.

On Friday, shortly after the Federal Bureau of Investigation (FBI) said North Korea was responsible for a cyberattack on Sony, President Obama promised: "They caused a lot of damage, and we will respond. We will respond proportionally, and we'll respond in a place and time and manner that we choose."

The U.S. government declined to directly address the outage.

"As the President said, we are considering a range of options in response," Marie Harf, a State Dept. spokeswoman said at a scheduled briefing on Monday morning.

"We aren't going to discuss 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. So I can't confirm those reports, but in general, that's what the President has spoken to," she said.

If it is an attack, it could just as easily be coming from an Internet hacking group angry at the country's alleged role in the attack on Sony. North Korea has been in the past a target for hackers who launched distributed denial of service attacks against the country, causing Internet connection problems.

But Monday's issues could also be due to something more mundane, like software problems or a failing router.

Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com