Kim's statement comes after North Korea sent troops and weapons to support Russia in the over three-year-long war in Ukraine.
Video clips broadcast by the state TV channel KCTV show how soldiers from artillery units fire grenades into the sea. Kim is seen looking through binoculars from an observation post.
He urged the soldiers to be ready "for real war" "at any time" and to be able to "annihilate the enemy in every battle", reports the North Korean news agency KCNA.
South Korean and Western intelligence services have reported that Pyongyang sent more than 10,000 soldiers to the Russian Kursk region last year, along with artillery grenades, missiles and long-range rockets.
Around 600 North Korean soldiers have been killed and thousands more have been injured in battles on Russia's side, according to information from Seoul.
