The politician laid flowers at a monument in Warsaw to the victims of the Volyn massacre on its 73th anniversary, Censor.NET reports citing The Daily Mail quoting AP.
"We must never let this crime against Poles and any such crime be overlooked, relativized or described as anything but genocide," he said.
As reported, several days earlier, Ukrainian President Petro Poroshenko also visited the memorial site to pay tribute to the Polish victims, accompanied by Ukrainian pilot and lawmaker Nadiia Savchenko.
Though older Poles still harbor bitter memories about the killings, overall ties remain strong between Poland and Ukraine, both countries that were formerly under Moscow's sway and which have sought closer ties with the West.
Related materials: Volyn tragedy