Kyiv, Ukraine - Ukraine's Western allies have not adequately responded to the involvement of North Korean troops in Russia's war with Kyiv, President Volodymyr Zelensky said in an interview released Thursday.

The comments came after the US and South Korean defense 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 Ukrainian forces.

Russian President Vladimir Putin is "testing the reaction of the West, of NATO states and the reaction of South Korea," the Ukrainian leader said in an interview with the South Korean television channel KBS.

"And if there is nothing – and I think that the reaction to this is nothing, it has been zero – then the number of North Korean troops on our border will be increased," he added.

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Seoul has long accused the nuclear-armed North of sending weapons to help Moscow fight Kyiv and alleges that Pyongyang moved to deploy soldiers en masse after its leader Kim Jong Un signed a mutual defense deal with Putin in June.

"I am surprised by China's silence. I am not saying that China is on our side, but it is one of the guarantors of security in your region, at least that's what we thought," Zelensky said, adding, "and there is this silence now."

"I think, Japan, South Korea – you are both strong countries – should reach out to China and have China as an ally in terms of what North Korea is doing now," he added.

"North Korea is now dragging your whole region into a war," the Ukrainian leader said.

His office released the comments as the US and South Korea held high-level talks after North Korea test-fired one of its newest and most powerful missiles, demonstrating its threat to the US mainland days ahead of elections.