Ukraine on Thursday said it had received the bodies of 261 fallen soldiers from Russia, while Moscow said 24 bodies had been handed over by Kiev.
Ukraine's office for the treatment of prisoners of war said investigators and forensic specialists would now work to identify the dead, after Moscow said the remains could be of Ukrainian soldiers.
The exchange was mediated by the International Committee of the Red Cross. The most recent handover of bodies had taken place in July.
Along with prisoner exchanges and family reunifications, such repatriations constitute the few remaining humanitarian contacts between the warring parties.
Independent experts estimate that hundreds of thousands of soldiers have been killed so far in Russia's war on Ukraine, which has been ongoing for nearly four and a half years.
For years now, Russia has not published figures on its own military dead. For Ukraine, President Volodymyr Zelensky said in February that 55,000 defenders had been killed. Experts believe the true figure is significantly higher.