Western officials have warned that such a development would stoke the almost three-year war and bring geopolitical consequences as far away as the Indo-Pacific region.
Zelenskiy said Ukrainian intelligence had determined that "the first North Korean military will be used by Russia in combat zones" between Sunday and Monday.
He said on Telegram that the deployment was "an obvious escalating move by Russia".
I received a report from Commander-in-Chief Syrskyi on the current situation at the frontline, with particular focus on the Pokrovsk, Kurakhove, and Lyman directions. In the Donetsk region, the situation remains difficult, but our combat brigades are holding their positions and…— Volodymyr Zelenskyy / Володимир Зеленський (@ZelenskyyUa) October 25, 2024
He didn't provide any further details, including where the North Korean soldiers may be sent.
Russia has been conducting a ferocious summer campaign along the eastern front in Ukraine, gradually compelling Kyiv to surrender ground.
But Russia has struggled to push Ukrainian forces out of its Kursk border region following an incursion almost three months ago.
North Korean units were detected on Wednesday in Kursk, according to Ukraine's Main Intelligence Directorate, known by its acronym GUR.
The soldiers had undergone several weeks of training at bases in eastern Russia and had been equipped with clothes for the upcoming winter, GUR said in a statement late Thursday.
It estimated the number of North Korean soldiers sent by Pyongyang to Russia at around 12,000, including some 500 officers and three generals.
GUR provided no evidence for its claims.
The deployment of North Korean forces under a military pact between Moscow and Pyongyang brings a new dimension to the conflict, which is Europe's biggest war since World War II and has cost tens of thousands of lives on both sides, including many civilians.
The US said Wednesday that 3000 North Korean troops have been deployed to Russia and are training at several locations, calling the move very serious.
President Volodymyr Zelenskiy says a third nation wading into the conflict makes it a world war. (AP PHOTO)
Zelenskiy said a week ago that his government has intelligence information that 10,000 troops from North Korea are being readied to join Russian forces fighting against his country.
He said that a third nation wading into the hostilities would turn the conflict into a "world war".
North Korea had already been supplying ammunition to Russia under a defence pact, but putting boots on the ground could severely complicate a war that has inflamed international politics, with most Western countries supporting Kyiv.
Russian President Vladimir Putin, meanwhile, has looked for support among BRICS countries.
5°C