North Korea suffered an Internet shutdown for at least two hours on Saturday, Chinese state-media and cyber experts said, after Pyongyang blamed Washington for an online blackout earlier this week.

"At Pyongyang time 7:30 pm (1030 GMT) North Korea's Internet and mobile 3G network came to a standstill, and had not returned to normal as of 9:30 pm," Xinhua news agency reported.

Xinhua's reporters in North Korea found that the Internet was "very unstable" throughout the day, the report added.

Respected cyber security firm Dyn Research also said on Twitter that North Korea suffered a "country-wide Internet blackout" on Saturday.

North Korea earlier in the day called US President Barack Obama a "monkey" for inciting cinemas to screen a comedy featuring a fictional plot to kill its leader, and blamed Washington for an Internet blackout this week.

The isolated dictatorship's powerful National Defence Commission (NDC) threatened "inescapable deadly blows" over the film and accused the US of "disturbing the Internet operation" of North Korean media outlets.

The earlier Internet outage triggered speculation that US authorities may have launched a cyber-attack in retaliation for the hacking of Sony Pictures -- the studio behind madcap North Korea comedy "The Interview".

Washington has said the attack on Sony was carried out by Pyongyang.