North Korea accused the US and South Korea of carrying out cyber attacks against its internet servers, causing official North Korean websites to become inaccessible.

The sites included those of the state-owned Korean Central News Agency (KCNA), Rodong Sinmun newspaper, and Air Koryo airline.

According to Russian news agency Itar-Tass, a ‘powerful hacker attack’ had brought down internet servers.

KCNA blamed the US and the South Korea for the attack, calling it a "cowardly and despicable act" motivated by fear.

"Intensive and persistent virus attacks are being made every day on Internet servers operated by the DPRK," KCNA said.

North Korea, also known as the Democratic People’s Republic of Korea (DPRK), has threatened to wage a nuclear war with the US, following new sanctions over it by the United Nations after its latest nuclear test.

South Korea previously accused North Korea of a cyber attack on its government run bank server in 2011.

North Korea was also held responsible for crashing websites of government agencies and businesses in South Korea.

Last week, US intelligence agencies reprted that cyber attacks have overtaken terrorism as the top security threat facing the United States.