President Volodymyr Zelenskiy called on Ukraine's allies to stop "watching" and take action to tackle the presence of North Korean troops in Russia before they start confronting his country in combat.
Zelenskiy, in a video posted on Telegram, said North Korea had made progress in its military capability, missile deployment and weapons production and "now unfortunately they will learn modern warfare".
"The first thousands of soldiers from North Korea are near the Ukrainian border. Ukrainians will be forced to defend themselves against them," he said. "And the world will watch again."
Zelenskiy said Ukraine had pinpointed every location where North Korean soldiers were posted in Russia. But Kyiv's Western allies, he said, had not supplied the long-range weapons needed to strike them.
"But instead of such necessary long-range capability, America watches, Britain watches, Germany watches...," he said.
"Everyone in the world who truly wants the Russian war against Ukraine not to expand....must not just watch. They must act. Words about the inadmissibility of escalation and expansion of war must be matched with actions."
The slick three-minute video interspersed his comments with images of North Korea's soldiers and missile launches as well as images of the war and the United Nations.
The video follows an interview with South Korea's KBS television on Thursday in which Zelenskiy blasted what he described as his allies' "zero" response to Russia's deployment of North Korean troops.
US Secretary of State Antony Blinken said on Thursday there were 10,000 North Korean troops in Russia, including as many as 8,000 in the southern Kursk region where Ukrainian forces launched an incursion in August.
North Korean Foreign Minister Choe Son Hui told his Russian counterpart Sergei Lavrov on Friday that his country would back Russia until it achieved victory in the Ukraine war.
