Russia might take the provocative step of putting Ukrainian soldiers on trial as Kyiv marks 31 years of independence next week, Ukraine's President Volodymyr Zelenskyy warned Sunday.

Zelenskyy cited media reports that Russia was preparing to put Ukrainian fighters captured during the siege of Mariupol on a public trial to coincide with the independence anniversary Wednesday.

"If this despicable court takes place, if our people are brought into these settings in violation of all agreements, all international rules, there will be abuse," Zelenskyy warned in an evening address.

"This will be the line beyond which no negotiations are possible."