Kim gave field guidance on Wednesday at Kim Jong Il University of Military and Politics, named after his father who died in 2011, which KCNA said is the "highest seat of military education" in the country.
North Korea has stepped up weapons development in recent years under Kim and has forged closer military and political ties with Russia, allegedly aiding Moscow in its war with Ukraine in return for help with strategic military projects.
Kim told university staff and students that "if the enemy opts for military confrontation with the DPRK, the DPRK will deal a death-blow to the enemy without hesitation by mobilizing all means in its possession," KCNA reported.
DPRK is short for the Democratic People's Republic of Korea, the North's official name.
"Outlining the complicated international situation ... and the uncertain and unstable military and political situation around the DPRK, he said that now is the time to be more thoroughly prepared for a war than ever before," KCNA said.
Earlier this month, Kim supervised the test launch of a new hypersonic intermediate-range ballistic missile using solid fuel, which analysts said would bolster the North's ability to deploy missiles more effectively than liquid-fuel variants.
North Korea has accused the United States and South Korea of provoking military tensions by conducting what it called "war maneuvers" as the allies have conducted military drills with greater intensity and scale in recent months.
