(Reuters) -Ukrainian President Volodymyr Zelenskiy vowed on Sunday to press on with prisoner exchanges with Russia and said any failure by Moscow to uphold humanitarian accords cast doubt over U.S. and other efforts to end the more than three-year-old conflict.

Russian officials say that Moscow is still awaiting confirmation from Kyiv on a planned exchange of 6,000 bodies of soldiers killed in action and is accusing Ukraine of delaying the process

Russia said Sunday that trains carrying more bodies of Ukrainian soldiers were due to depart towards the Ukrainian border, escalating a spat with Kyiv over a prisoner of war swap.