Pyongyang, North Korea - North Korean leader Kim Jong-un has dismissed his top general and called for stepping up war preparations "in an offensive way", including boosting weapons production and conducting more drills, state media reported Thursday.

With a cigarette in hand, Kim was shown talking to a room full of uniformed top generals, and pointing at maps, images in state media showed, while he discussed "major military actions" against South Korea at a meeting of the Central Military Commission.

The Korean Central News Agency said the agenda of the meeting, which comes just days after Kim inspected key arms factories, was "the issue of making full war preparations" and ensuring "perfect military readiness for a war".

The meeting comes as Seoul and Washington prepare for more major joint drills later this month, which the North views as rehearsals for invasion and has repeatedly warned could trigger "overwhelming" action in response.

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At the meeting, Kim dismissed chief of the general staff Pak Su-il, replacing him with Vice Marshal Ri Yong-gil, KCNA said without giving further details.

Pak, who was promoted to the post late last year, may have been dismissed "because he did not demonstrate sufficient competence in the field of military operations," according to Cheong Seong-chang, a researcher at the Sejong Institute.

"Kim Jong Un has shown a tendency to quickly replace officials when they are judged to be lacking in the ability to control and perform their duties," he said.

Ri may have been the "most suitable person" to replace Pak, as he has previously held the position for a long time, Cheong added.

Kim called for "all the munitions industrial establishments to push ahead with the mass-production of various weapons and equipment," the North Korean report said.

"He also called for actively conducting actual war drills to efficiently operate (the) newly deployed latest weapons and equipment," it added.

Kim was said to have reached an "important conclusion on further stepping up the war preparations of the KPA in an offensive way."

The latest KCNA report appeared to be North Korea's "own response to the upcoming joint military training between Seoul and Washington," an official from Seoul's unification ministry told reporters.

Referring to photos carried by the North's Rodong Sinmun newspaper showing Kim pointing to what appeared to be a map of Seoul, he said: "I think he wanted to send a message to the South with a threatening action."