 The Ukrainian and Polish presidents marked the anniversary of massacres of Poles by Ukrainian nationalists during World War II on July 9, killings that have been a source of tension between the Allies. Volodymyr Zelensky and his Polish counterpart Andrei Duda attended a church service held in memory of the victims in the western Ukrainian city of Lutsk. Warsaw has positioned itself as one of key of staunchest supporters since Russia invaded the country in 2022. However, the Volodymyr massacre, in which historians say tens of thousands of Poles perished, has continued to hang over ties between the two nations and become more prominent ahead of the July 11 anniversary of one of the bloodiest days of a series of killings that took place from 1943 to 1945. Polish historians say that up to 12,000 Ukrainians were also killed in Polish retaliatory operations. The massacre caused an unusually public row between Poland and Ukraine earlier this year, after a Polish foreign ministry spokesman said that Zelensky should apologize and ask for forgiveness for the events in Bolonia.