Leader Kim Jong Un oversaw the test of the Hwasong-19 missile, which flew higher and further than any previous missile, according to the North and to Seoul and Tokyo's militaries, which tracked it in real time.

The official Korean Central News Agency hailed it as "the world's strongest strategic missile" and leader Kim "expressed great satisfaction" at the successful launch.

Developing advanced solid-fuel missiles -- which are quicker to launch and harder to detect and destroy -- has long been a goal for Kim.

The test proved that North Korea's "development and manufacture of nuclear delivery means... is absolutely irreversible", according to KCNA.

The missile is now a "perfected weapon system", the agency said, with Kim describing the launch as an "appropriate military action" to send a message to the country's rivals.

North Korea "would never change its line of bolstering up its nuclear forces," it said.

State media released pictures of the ICBM and Kim observing the test in his signature black leather jacket, accompanied by his daughter, Kim Ju Ae, who Seoul's spy agency recently said was being groomed as Kim's heir.

The launch came just hours after US and South Korean defence chiefs called on Pyongyang to withdraw its troops from Russia, warning that North Korean soldiers in Russian uniforms were being deployed for possible action against Ukraine.

Experts said the missile test seemed to have been carried out to divert attention from mounting international criticism over the purported troop deployment to Russia.

The North has denied the move, but the United States said Thursday that up to 8,000 North Korean troops had reached Russia's border region with Ukraine, trained and ready for combat.

South Korean Defense Minister Kim Yong-hyun also said on Thursday that in addition to troops, North Korea has sent more than 1,000 missiles to Russia as well as millions of munitions.

Seoul has long accused the nuclear-armed North of sending weapons to help Moscow fight Kyiv and alleged that Pyongyang has moved to deploy soldiers en mass in the wake of Kim Jong Un's signing of a mutual defence deal with Russian President Vladimir Putin in June.