According to Press TV, the order announced on Friday came a day after the UN approved its harshest sanctions crafted by the US against the impoverished nation, marking a further escalation of tension on the Korean peninsula.
The official KNCA news agency said under Kim’s order, nuclear warheads must be “on standby so as to be fired at any moment.”
He issued the order while supervising military exercises involving newly developed rocket launchers, the news agency added.
Kim said the situation had become very dangerous following the adoption of the sanctions, which came just days ahead of joint military drills by the US and South Korea.
Pyongyang views the drills as provocative rehearsals for an invasion.
North Korea launched several projectiles into the sea about 150 kilometers (90 miles) off the South Korean coast on Thursday in an apparent response to the new sanctions.
Following the adoption late Wednesday of the US-engineered sanctions, South Korean President Park Geun-hye warned of a “fiercer” North Korean backlash than normal.
On Friday, however, Park promised a harsh response to any military provocation by North Korea.