International Desk

North Korea on Thursday launched one of its most powerful missiles, South Korea's military said, Kim Jong Un's first weapons test since being accused of sending soldiers to Russia.

Seoul had warned a day earlier that the nuclear-armed North was preparing to test-fire another intercontinental ballistic missile (ICBM) or even conduct a nuclear test ahead of next week's US elections.

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.

Seoul's military said early Thursday it had "detected one long-range ballistic missile" fired from near Pyongyang, adding it travelled around 1,000 kilometres (621 miles) after being fired on a lofted trajectory.

The Joint Chiefs of Staff said it had tracked preparations for the launch in real-time with allies Tokyo and Washington, and that it would respond with "joint exercises involving US strategic assets," which always infuriate the North.

Tokyo also confirmed the launch, with Japan's defence minister saying it was an "ICBM-class" missile that flew for longer than any other previously tested by the North.

The missile was airborne for about 86 minutes and achieved an altitude of 7,000 kilometres, according to Tokyo.

"This ballistic missile had the longest flying time, and we estimate that its flying altitude was the highest we have seen," Japanese defence minister Gen Nakatani told reporters.

North Korea typically test-fires its longest-range and most powerful missiles on a so-called lofted trajectory -- fired up, not out -- which it says is to avoid overflying neighbouring countries.

- Diverting attention? -

North Korea's missile launch "seems to have been carried out to divert attention from international criticism of its troop deployment," Yang Moo-jin, president of the University of North Korean Studies in Seoul, told AFP.

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.

South Korea has said the troop deployment poses a "significant security threat", and its spy agency has flagged domestic issues for the North stemming from the move, with the families of soldiers reportedly grief-stricken at the news.

With the ICBM launch, "North Korea may also be trying to redirect the anxiety of military families, including those of deployed personnel," Yang added.

South Korea's military told lawmakers on Wednesday that preparations were "nearly complete for an ICBM-class long-range missile" and that a launch could be aimed at testing the North's atmospheric reentry technology.

Seoul has long warned that Russia may be providing new technology or expertise to Pyongyang in return for weapons and troops to help them fight Ukraine.

It is possible "Russia actually provided new technology for re-entering the atmosphere," which would mean the launch was of a new model of ICBM, Ahn Chan-il, a defector-turned-researcher who runs the World Institute for North Korea Studies, told AFP.

But it is more likely that Thursday's test was a bid to distract from the troop deployment and get "the world's attention ahead of the US presidential election" rather than experimenting with new technology, Ahn added.

Seoul, a major weapons exporter, has said it is reviewing whether to send weapons directly to Ukraine in response, something it has previously resisted due to longstanding domestic policy that prevents it from providing weaponry into active conflicts.

North Korea has denied sending troops, but in the first comment in state media last week, its vice foreign minister said that if such a deployment were to happen, it would be in line with international law.

Pyongyang is banned from tests using ballistic technology by multiple rounds of UN sanctions, but leader Kim has ramped up launches this year, with experts warning he could be testing weaponry before providing it to Russia.