North Korean leader Kim Jong Un has called for an increase in missile production to help secure "overwhelming military power" and be ready for war, state media KCNA said on Monday, as South Korea and the United States gear up for annual military drills.

Kim gave the order as he visited key munitions factories that produce tactical missiles, missile launch platforms, armored vehicles and artillery shells on Friday and Saturday.

His field inspection was the latest in a string of visits to arms factories, where he ordered the mass production of weapons, and came days before South Korea and the U.S. are to begin annual military drills, which Pyongyang sees as a rehearsal for war.