The three-day inspection of the factories comes less than two weeks after Kim attended a major military parade with Russian and Chinese officials, showcasing North Korea's newest weapons, including intercontinental ballistic missiles and spy drones.

Kim visited a factory producing engines for armed unmanned aerial vehicles, as well as production lines of shells for super-large-calibre multiple rocket launchers and transporter-erector-launchers, the Korean Central News Agency reported.

During the engine factory visit, Kim called for "steadily increasing the performance and reliability of the engine" and "rapidly expanding its production capacity", KCNA said.

Kim also highlighted the modernisation of small arms as "the most important and urgent matter in making war preparations... in keeping with the changed aspect of war", the agency reported.

The inspections come as South Korea and the United States prepare for major joint military drills later this month.

North Korea views such exercises as rehearsals for an invasion and has repeatedly warned it would take "overwhelming" action in response.

Last month, Pyongyang held a major military parade to mark the 70th anniversary of the Korean War armistice, with analysts describing the event as "the largest, most overt North Korean display of nuclear-capable systems".

North Korea also recently held a large defence expo, with Kim giving a tour to the visiting Russian defence minister through a vast display of the country's newest and most advanced weaponry, including ballistic missiles and spy drones.