Zelensky said on Wednesday that Kyiv had details of 155 Chinese nationals who had been deployed to assist Moscow's invasion, a day after claiming the Ukrainian army had captured two Chinese soldiers in the eastern Donetsk region.

Asked about Zelensky's assertion on Thursday, Beijing's foreign ministry told "relevant parties" to "refrain from expressing irresponsible remarks".

"We would advise the relevant parties to recognise China's role correctly and clear-headedly," ministry spokesman Lin Jian said at a regular news briefing, without mentioning Ukraine or Zelensky by name.

China has portrayed itself as a neutral party in the grinding three-year war despite criticism from Western governments that its close ties to Russia have given Moscow crucial economic and diplomatic support.

Zelensky said on Wednesday that the "overt involvement of Chinese citizens in combat operations... is a deliberate step towards expanding the war".

"They drag other countries into war," Zelensky said of Russia.

"I believe that they are now dragging China into this war."

Lin said Beijing "has always required that its nationals... avoid involving themselves in armed conflicts in any form".

"China is not a creator of or party to the Ukraine crisis. We are staunch supporters and active promoters of a peaceful resolution," he said.