朝鲜指责美国发动网络攻击

North Korea is accusing the United States of launching cyber attacks against it, after several of Pyongyang's state-controlled websites suffered apparent outages this week.

The official Korean Central News Agency (KCNA) on Friday blamed the U.S. and its allies for what it called "concentrated and persistent virus attacks" over the past several days.

Internet users say several state-controlled websites, including KCNA, have been inaccessible for unusually prolonged periods this week. The U.S. has not responded to the accusation.

The North Korean article offered few details, but attempted to link the alleged cyber attack to a computer-based joint U.S.-South Korean war simulation that began earlier this week.

Last week, North Korea threatened to wage a "preemptive nuclear attack" on the U.S. if it went ahead with the annual exercise, which proceeded as normal on Monday.