(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.

Russia claims Ukraine indefinitely postponed the release while Kyiv maintains it has been delayed until next week.

Russian officials say that Moscow is still awaiting confirmation from Kyiv on a planned exchange of 6,000 bodies of soldiers killed in action.