SEOUL, South Korea -- North Korean leader Kim Jong Un called for a "drastic boost" in missile production during visits to key weapons factories, state media said Monday, as South Korea and the United States prepared for joint drills next week.

The tour of the plants from Friday to Saturday came after Kim called for stepping up war preparations at a key military meeting last week.

Kim's two-day inspections included visits to factories producing tactical missiles, large-calibre control multiple rocket launcher shells, as well as armoured combat vehicles, the Korean Central News Agency (KCNA) reported.

During the tactical missile factory visit, Kim "expressed satisfaction" as the plant had "perfected the scientific and technological issues arising in production" and pushed ahead with the modernisation of the weapons.

"He set forth an important goal to drastically boost the existing missile production capacity" and underlined the factory's role in "speeding up" war preparations, KCNA said.

Kim stressed the "need to ensure boost in the production of shells" and personally drove a armoured combat vehicle, according to the report.

Photos carried by the official Rodong Sinmun newspaper showed a beaming Kim seated in the driver's seat of a "newly-developed utility combat armoured vehicle" as he took it out for a test drive surrounded by three officials.

Kim also inspected a factory producing transporter erector launchers -- vehicles for transporting and launching tactical missiles -- and stressed the importance of developing and producing the mobile platorms.

The North Korean army should have an "overwhelming military force" and be "fully prepared for coping with any war at any moment" against the enemy, Kim said, adding they must "surely annihilate them if they launch an attack," KCNA reported.

The inspections come as South Korea and the United States prepare for the annual Ulchi Freedom Shield (UFS) exercise set to take place August 21 through August 31.

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

Seoul's Joint Chiefs of Staff on Monday described the upcoming joint drills as "a tough and realistic exercise to strengthen the combined defence posture and alliance response capabilities."

Leaders from South Korea, the United States, and Japan are also set to hold a trilateral summit in Washington on Friday, as they seek to bolster security cooperation in response to North Korea's growing nuclear and missile threats.

Last week, Kim presided over a meeting with key military officials, calling for stepping up war preparations "in an offensive way" including boosting weapons production and conducting more drills.