Major North Korean websites have been out of action for 10 straight days, according to reports Friday.
The websites hosted on Chinese servers have not been accessible since June 3, Yonhap News Agency reported. They include Pyongyang's propaganda website, Uriminzokkiri, websites of Kim Il-sung Broadcasting University and DPRK Today.
"Web servers are running with no disruption, but we are not sure of the reason why the websites are unreachable," an official of Xinwang, a Chinese server management company, was quoted as saying. Xinwang hosts the server of Uriminzokkiri.
But websites of Pyongyang's state newspaper, Rodong Sinmun, and state-controlled media outlet KCNA are operating. Their servers are allegedly hosted inside North Korea.
The problem's cause has not been verified, but some experts suggested a possible cyberattack.
It is not North Korea's first Internet outage. It was disrupted for eight days in December, a few days after U.S. President Barack Obama warned of a "proportional response" to North Korea following the North's alleged hacking of Sony Pictures.
Rep. Michael McCaul, chairman of the House Homeland Security Committee, virtually admitted in March that December's Internet blackout was payback for the Sony hacking.
In November, a group of hackers broke into the computer networks of Sony Pictures Entertainment and released emails of its senior executives and personal information about employees. They demanded that "The Interview," a film comedy that portrayed the assassination of North Korean leader Kim Jong-un, not be released.
The FBI stood by its conclusion that North Korea was behind the cyber attack, though the reclusive nation strongly denied involvement.