"China is verifying the relevant information and circumstances," foreign ministry spokesman Lin Jian said when asked about the prisoners of war.

Beijing urged "relevant parties to accurately understand China's objective and impartial stance, and to refrain from political manipulation and hype", Lin said.

Ukraine on Monday held a press conference at which Chinese prisoners of war under armed guard told journalists they hoped to be swapped and warned other Chinese nationals not to go to fight.

Zelensky said Friday that several hundred Chinese nationals were fighting at the front line alongside Russia.

But Beijing insisted Tuesday that it had "repeatedly issued safety advisories, urging Chinese citizens to stay away from areas of armed conflict and to avoid becoming involved in conflict in any form".

"With regard to the individual actions and consular cases involving Chinese citizens overseas, China handles them in accordance with the law," Lin said.

China presents itself as a neutral party in the Ukraine war and says it is not sending lethal assistance to either side, unlike the United States and other Western nations.

But China is a close political and economic ally of Russia, and NATO members have branded Beijing a "decisive enabler" of the war, which it has never condemned.