North Korea has threatened to stage a "sacred war" over U.S.-South Korean annual joint military exercises next week, denouncing the drill as a "silent declaration of war", AFP reported.

The North's National Defense Commission (NDC) on Saturday, Feb 25, described the exercise as "unpardonable war hysteria" and said its army and people would "foil" the U.S. and South Korean moves with "a sacred war of our own style".

The threat is the latest instance of Pyongyang taking a hostile tone towards Seoul since Kim Jong-Un, the youngest son of the late leader Kim Jong-Il, took over following the death of his father in December.

Last week the North vowed "merciless retaliatory strikes" if any shells landed in waters claimed by Pyongyang during a live-fire artillery exercise near the disputed Yellow Sea border.

But in the event it took no military action in response to the drill.

The United States and South Korea are to begin two major annual joint military exercises in the coming week.

Key Resolve, a computerized command post exercise, will start on Monday and continue until March 9. Separately, the joint air, ground and naval field training exercise Foal Eagle will be held from March 1 to April 30.

"Key Resolve and Foal Eagle are unpardonable war hysteria kicked up by the hooligans to desecrate our mourning period and an unpardonable infringement upon our sovereignty and dignity," the NDC said in a statement.

"Our army and people will foil the moves of the group of traitors to the nation and warmongers at home and abroad for a new war with a sacred war of our own style," the NDC said, indicating it would stage a counter exercise.

"War maneuvers... are, in essence, a silent declaration of a war. The declaration of the war is bound to be accompanied by a corresponding physical retaliation," it said.

"Now that a war has been declared against us, the army and people are firmly determined to counter it with a sacred war of our own style and protect the security of the nation and the peace of the country," the NDC said.

It flexed its muscle against "U.S. imperialists" accusing Washington of intensifying moves to ignite a war.

"Nuclear weapons are not the monopoly of the U.S. We have war means more powerful than the U.S. nukes and ultra-modern striking equipment which no one has ever possessed," it said.

"The US is sadly mistaken if it thinks it is safe as its mainland is far away across the ocean. There is no limit to the striking intensity and range of our army and people to wipe out the aggressors," it added.