North Korea, North Korea - North Korean leader Kim Jong-un oversaw the firing of "cutting-edge" hypersonic missiles as he ramped up the preparation of nuclear forces for war, state media reported Monday.

Seoul and Tokyo said Sunday they had detected the launch from near Pyongyang of two ballistic missiles – the country's first test of the year just hours before South Korean leader Lee Jae Myung headed to Beijing for a summit.

On Monday, the Korean Central News Agency (KCNA) quoted Kim as saying the test showed "the readiness of the DPRK's nuclear forces."

"Important achievements have been recently made in putting our nuclear forces on a practical basis and preparing them for an actual war," Kim insisted, per KCNA.

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Pyongyang's ramped up military activity, he said, was "aimed at gradually putting the nuclear war deterrent on a high-developed basis."

Photos shared by state media showed Kim puffing on a cigarette accompanied by top officials as a missile soars into the early morning sky.

"Why it is necessary is exemplified by the recent geopolitical crisis and complicated international events," Kim reportedly said, in a clear reference to the violent overthrow of Venezuelan President Nicolas Maduro by the US.

North Korea on Sunday condemned the attack as a "serious encroachment of sovereignty" that "clearly confirms once again the rogue and brutal nature of the US".

The weapons system highlighted on Monday was first tested in October.

Hypersonic missiles travel at more than five times the speed of sound and can maneuver mid-flight, making them harder to track and intercept.