North Korea on Friday accused the United States and South Korea of carrying out a "persistent and intensive" cyber attack against its official websites in recent days.

A number of official North Korean websites, including those of the Korean Central News Agency (KCNA), the daily Rodong Sinmun newspaper, and Air Koryo airline became inaccessible early Wednesday.

"Internet servers operated by our republic have come under daily cyber attack(s) which are persistent and intensive", said KCNA, which noted that the problem coincided with an ongoing South Korea-US joint military drill.

Accusing the United States and its South Korean "puppets" of building up their cyber-war capabilities, KCNA said the attack was a "cowardly and despicable act" motivated by fear.

Military tensions on the Korean peninsula have escalated dramatically since the North conducted its third nuclear test last month.

Pyongyang responded to the subsequent UN sanctions -- and joint military exercise -- with threats of "all-out war" backed by nuclear weapons.

"We'll never sit idle in the face of such cyber attacks by the enemy... which have reached an extremely reckless and grave stage," KCNA said.

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