By Max Hunder and Pavel Polityuk ODESA, Ukraine/KYIV (Reuters) -Dozens of Ukrainian prisoners of war appeared to have been killed when a prison building was destroyed in a missile strike or explosion, with Moscow and Kyiv accusing each other of responsibility on Friday. The deaths, some of which were confirmed by Reuters journalists at the prison where the men were held, overshadowed U.N.-backed efforts to restart shipping grain from Ukraine and ease a looming global hunger crisis. Russia’s defence ministry said 40 prisoners were killed and 75 wounded in Thursday’s attack on the prison, in the…