Volodymyr Zelensky has claimed 50,000 North Korean soldiers have arrived in Russia to study the war in Ukraine.
The Ukrainian leader, who remains at war with Russia following Vladimir Putin's illegal invasion in February 2022, also said North Korean missiles had been detected in the ex-Soviet state.
Mr Zelensky suggested officials in Kyiv have opened up conversations with their counterparts in South Korea amid a push for closer cooperation.
Speaking to local media outlet United News, Mr Zelensky said: "North Koreans appear on the territory of the Russian Federation from time to time.
"We see this, we know this. At first, we were talking about hundreds, then thousands, and now a decision has been made for 30,000 to 50,000 North Koreans to be deployed on the territory of Russia.
"They are studying this war. If we are talking about crises and escalation in another region – in the Pacific – which could pose a threat to other Asian countries, then North Korea will certainly gain experience in modern warfare under Russia.
"We have already found North Korean missiles on the territory of Ukraine. Today, this is already an established fact.
"It is absolutely clear that North Korea will continue to build its experience in modern warfare, receive licenses from Russia, and receive all kinds of military tools from them. We understand this very clearly."
Vladimir Putin has lost more than one million troops in Ukraine
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Mr Zelensky's warning follows earlier reports that Russia had been preparing facilities in its Voronezh region since June to receive fresh North Korean deployments.
Officials believe Russia deploys its North Korean missile unit in Russia's Voronezh Oblast.
Russia also used a North Korean missile on July 30 as President Putin's troops carried out a strike near Kryvyi Rih.
Another crater from a North Korean KN-23 ballistic missile was found in a field a short time later.
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North Korean soldiers have been deployed in the conflict
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Russia continues to mount its onslaught against Ukraine despite more than 1.1 million soldiers being killed or wounded.
President Putin retains a close relationship with North Korean dictator Kim Jong Un, with the pair finalising a deal to secure long-term military cooperation in April 2026.
The 2024 treaty between Moscow and Pyongyang obliges both nations to provide military assistance "without delay" if either is attacked.
The North Korean supreme leader has continued to publicly back the Kremlin, pledging in a letter to Putin that his country's support would remain "unshakeable".
Russia continues to bombard strikes on Ukraine
|REUTERS
Pyongyang earned between $7.7billion and $14.4billion from military cooperation with Russia from August 2023 to the end of 2025, a study by South Korea's Institute for National Security Strategy estimated in March.
Analysts have said North Korea's exports of military hardware to Russia have surged, with shipping containers reportedly reaching 33,000 by March 2026.
Around 11,000 North Korean troops were stationed in Russia's Kursk Oblast at the start of 2026, according to South Korean intelligence.
However, around 6,000 North Korean soldiers have also died in the conflict as of March this year.
Volodymyr Zelensky suggested officials in Kyiv have opened up conversations with their counterparts in South Korea amid a push for closer cooperation
| REUTERSSoldiers who complete tours on the frontline are reportedly rotated home, with many becoming instructors who pass on battlefield lessons to the wider North Korean army.
Nearly 3,000 troops had returned to North Korea by early 2026 under this rotation system.
Seoul has voiced growing unease over the scale of the cooperation, with its unification minister recently shifting the South's approach from "denuclearisation first" to "peace first".
The developments will add to concerns in Washington and Seoul that battlefield experience gained in Ukraine could be redirected towards a future crisis on the Korean peninsula.