The North Korean army on Wednesday threatened "merciless retaliation" against South Korea and the U.S. for their joint military exercises.

The U.N. and U.S. imposed new sanctions as punishment for the February nuclear test, moves to which the North responded by once again threatening a preemptive nuclear strike against the United States, an act far beyond its technical capability.

"The warmongers would be well-advised to keep in mind that the armistice agreement is no longer valid and our country is not restrained by the North-South declaration on non-aggression. What is left to be done now is an action of justice and merciless retaliation of the army and people of our country," said an unidentified KRT news reader, quoting a statement by the Ministry of the People's Armed Forces of North Korea's National Defence Commission.

North Korea has accused the United States of using the joint military drills in South Korea as a rehearsal for war and has threatened to scrap the 1953 armistice that ended hostilities in the 1950-53 Korean War.

North Korea's official media on Wednesday also broadcast video of its leader Kim Jong-un visiting military units near the border with the South.

The North's state news agency KCNA also said Kim visited military units on Monday.

Presented by Adam Justice