A planned exchange of Russian and Ukrainian prisoners of war failed to take place on Saturday, with Moscow accusing Kyiv of postponing the swap at the last minute, something Ukrainian officials dismissed as “dirty games” from the Kremlin. Russia said Ukraine unexpectedly postponed a transfer involving prisoners of war and the bodies of dead soldiers, leaving more than 1,200 frozen Ukrainian bodies waiting in refrigerated trucks at an exchange point with no one to collect them. Ukraine rejected Russia’s account of the events, saying that the two sides had agreed to exchange seriously wounded and young troops on Saturday but...