North Korea to soon unveil 'next-stage' nuclear plans, Kim says

North Korean leader Kim Jong Un will unveil plans to bolster his nuclear forces at an upcoming ruling party meeting, state media reported Wednesday, after a missile launch he said would bring "excruciating mental agony" to his enemies.

The landmark congress of North Korea's ruling Workers Party is expected in the coming weeks and is its first in five years.

Kim has ordered the "expansion" and modernisation of the country's missile production ahead of that meeting.

Overseeing a ballistic missile test on Tuesday, Kim said the party congress "will clarify the next-stage plans for further bolstering up the country's nuclear war deterrent", the state-run Korean Central News Agency (KCNA) said.

Kim, accompanied by senior North Korean officials as well as his young daughter, watched the test-firing of a "large-caliber" multiple rocket launcher that fired four missiles, KCNA said.

"The result and significance of this test will be a source of excruciating mental agony and serious threat to the forces that attempt to provoke a military confrontation with us," Kim said.

While acknowledging that development of the rocket launcher system had "not been plain sailing", Kim said the test was "of great significance in improving the effectiveness of our strategic deterrent".

Photos released by state media showed Kim and his daughter, who analysts believe is called Ju Ae, watching the missile launch.

The rockets "hit a target" in waters 358.5 kilometres (222.7 miles) away, according to the North Korean leader.

The ballistic missiles were fired toward the Sea of Japan, with two missiles landing outside the country's Exclusive Economic Zone, Japanese state news agency Jiji Press had reported, citing defence ministry sources.

Lee Ho-ryung, principal researcher at the Korea Institute for Defense Analyses, told AFP the upcoming congress would likely see Kim announce "that the goal is now to maximise nuclear operational prowess".

"Kim Jong Un has used past party congresses to stress the completion of the country's nuclear capability, and this time he is expected to declare that such capability has now reached its peak," she said.

- Second test in January -

The test was Pyongyang's second of the month, following a volley of missiles fired hours before South Korea's leader headed to China for a summit.

It followed a high-level visit to Seoul by the Pentagon's number three official, Elbridge Colby, who hailed South Korea as a "model ally".

Ties between the United States and South Korea, longstanding treaty allies, were forged in the bloodshed of the Korean War.

Washington still stations 28,500 troops in South Korea as a deterrent against the nuclear-armed North.

"Pyongyang may have been signalling to Washington that it possesses response capabilities on an entirely different level from those of countries such as Venezuela," Hong Min, an analyst at the Korea Institute for National Unification, told AFP.

Last month, Kim bashed Seoul's push to develop its own nuclear-powered submarines with the United States, calling it a "threat" that "must be countered".

During his first term, US President Donald Trump met with Kim three times, in an effort to reach a denuclearisation deal.