Polish Prime Minister Donald Tusk said he hopes Ukrainians will rethink their approach to the Volyn tragedy and urged people in Poland to avoid inflaming emotions. [The Volyn (Volhynia) tragedy was a series of events that led to the ethnic cleansing of the Polish and Ukrainian populations in 1943 during World War II. It was part of a long-standing rivalry between Ukrainians and Poles in what is now Ukraine's west. Poland considers the Volyn tragedy a genocide of Poles – ed.]

Poland, steeped in bad memories of the 1939 invasion and decades of Soviet dominance after World War II, is a firm backer of Ukraine’s defense against Russia. But a flare-up over…

Russia has the greatest interest in worsening relations between Poland and Ukraine and would be “overjoyed” if a deep political crisis were to arise between the two countries. —…