In an interview with South Korea’s public broadcaster KBS, the Ukrainian leader said he believed Moscow was already trying to agree for North Korea to send engineering troops and a “large number of civilians” to work at Russian military plants.

“Putin is checking the reaction of the West," Zelenskyy said. “And I believe that after all these reactions, Putin will decide and increase the contingent [...] The reaction that is there today is nothing, it is zero.”

He began publicly warning of North Korean involvement in the war on October 13. Western allies have since described the move as a major escalation, but have not announced retaliatory measures or said they are preparing to implement any.

In his interview comments, Zelenskyy said he was surprised by the “silence” of China, the world's second economy, over the troop deployment.

Russia has not denied the involvement of North Korean troops in the war. North Korea initially denied involvement, but has since defended the idea of deploying troops as being in line with international law.

Deputy U.S. ambassador to the United Nations Robert Wood told the Security Council on Thursday that Washington had received information indicating that “right now” there are 8,000 North Korean troops in Russia's southern Kursk region, which borders on northeastern Ukraine.

The direct tone of Zelenskyy’s rhetoric pointed to mounting Ukrainian frustration over the extent of Western support for Kyiv at a critical time in the war with Russia, with the clock counting down to Tuesday's U.S. presidential election.

Russian troops have been slowly advancing for months in eastern Ukraine and Kyiv’s outgunned and outnumbered forces have struggled to find a way to hold them back.