Poland says over 100,000 Poles were killed in the massacres by Ukrainian nationalists.
In 2013, the Polish parliament recognised the massacre by the Ukrainian Insurgent Army (UPA) during World War Two as "ethnic cleansing bearing the hallmarks of genocide".
Ukraine has not accepted that assertion and often refers to the Volhynia events as part of a conflict between Poland and Ukraine that affected both nations.
In 2017, Ukraine banned Polish authorities from searching for victims on its territory.
Tuesday's commemorations in Warsaw were attended by Ukraine's parliament speaker Ruslan Stefanchuk, who moved to defuse tensions in May when he told the Polish parliament that Kyiv understood Poland's pain.
Persons:
Ukraine's, Mateusz Morawiecki, Volodymyr Zelenskiy, Andrzej Duda, Ruslan Stefanchuk, Anna Wlodarczak, Alan Charlish, Nick Macfie
Organizations:
WARSAW, Ukrainian Insurgent Army, UPA, Kyiv, Thomson
Locations:
Poland, Ukraine, Volhynia, Russia, Warsaw, Soviet Union, Ukrainian, Lutsk