Some major North Korean websites remained blocked Wednesday for the second straight day amid growing speculation over cyber warfare between Washington and Pyongyang.

After going down on Tuesday evening, the website of the North's main propaganda organ, Uriminzokkiri, had remained inaccessible before going back online Wednesday afternoon, although no updated contents were posted.

Access to other well-known North Korean propaganda websites, including Ryugyong and Ryomyong, remained blocked as of Wednesday evening.

Yonhap News Agency found the Internet servers of the affected websites were all located in Chinese cities, including Shenyang and Dandong.

The location of the servers indicated the problem may be taking place in the network linking China and North Korea, some experts noted.

The Internet outage comes as speculation continued over who is responsible for the blockage.

A day earlier, the home pages of North Korea's key news media like the Korean Central News Agency and the Rodong Sinmun went down for nearly 10 hours before going back online in late morning. They went down again around midnight before resuming one hour later.

Internet performance analyst Dyn Research reported that the North Korean Internet had been down for one hour since 12:41 a.m.

The websites, which went down on Tuesday, were located in North Korea.

There has been speculation the U.S. may be behind the latest outage as it came just two days after U.S. President Barack Obama vowed to "respond proportionally" to the North's alleged hacking of Sony Pictures.

The North had warned of retaliation against Sony's plan to release the film "The Interview," which depicts an assassination attempt on North Korean leader Kim Jong-un.

The U.S. government has neither confirmed nor denied its role in the outage. (Yonhap)