Ukrainian President Volodymyr Zelensky speaks during joint press conference with Belgium Prime Minister in Kyiv on April 8, 2025. [AFP]
Moscow and Beijing have deepened political, military and economic cooperation since Russia invaded Ukraine in February 2022.
"Our military captured two Chinese citizens who fought in the Russian army. This happened on the territory of Ukraine -- in the Donetsk region," Zelensky said in a post on social media.
"We have the documents of these prisoners, bank cards, and personal data," Zelensky said in a post that included a video of one of the alleged Chinese prisoners.
There was no immediate response to the claims from either Moscow or Beijing.
China presents itself as a neutral party in the conflict and says it is not sending lethal assistance to either side, unlike the United States and other Western nations.
But it is a close political and economic ally of Russia and NATO members have branded Beijing a "decisive enabler" of Moscow's invasion, which it has never condemned.
US President Donald Trump has been pushing for a speedy end to the more than three-year war since taking office but his administration has failed to reach a breakthrough despite rounds of negotiations.
'Many more' Chinese soldiers
Kyiv has repeatedly urged Beijing to pressure Moscow to end its invasion that has cost tens of thousands of lives and yet still so far failed to see the Kremlin achieve its core objectives.
Zelensky said Kyiv had evidence that "many more Chinese citizens" are fighting alongside Russian forces.
"I have instructed the foreign minister of Ukraine to immediately contact Beijing and find out how China is going to respond to this," Zelensky said.
He said the capture of the two men and Moscow's involvement of China in the conflict were "a clear signal that Putin is going to do anything but end the war".
Zelensky also demanded "a reaction from the United States, Europe, and everyone in the world who wants peace" in his post online.
"I think the United States should pay more attention to what is happening today," he said separately at a press conference in Kyiv.
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Ukraine has been urging its Western partners to respond to the Russian deployment of thousands of North Korean troops to the western region of Kursk.
Ukraine has been struggling to hold ground after launching an offensive on the border region last year.