North Korea's Internet communications has been hit by a series of outages in the last 24 hours, a researcher claims. Websites hosted on servers in Pyongyang started to become unresponsive on Monday morning, said Doug Madory, director of Internet analysis at Dyn Research.

The news has led to speculation that it might be the result of a promised response by the U.S. to an attack against Sony Pictures.

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."

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.