KYIV: The Ukrainian and Polish presidents jointly marked the anniversary on Sunday of World War II-era massacres of Poles by Ukrainian nationalists, killings that have caused tension for generations between countries that are now close allies.

Warsaw has positioned itself as one of Kyiv’s staunchest supporters since Russia invaded the country in 2022.

But the Volhynia massacres have continued to hang over ties between the two nations, particularly ahead of the July 11 anniversary of one of the bloodiest days of a series of killings that took place from 1943 to 1945.

Poland says around 100,000 Poles were killed in the massacres by Ukrainian nationalists. Thousands of Ukrainians also died in reprisal killings.

Ukraine’s Volodymyr Zelenskiy and his Polish counterpart Andrzej Duda attended a church service together in the western Ukrainian city of Lutsk, in memory of the victims.

“Together we pay tribute to all the innocent victims of Volhynia! Memory unites us!,” Duda’s office and Zelenskiy both wrote on Twitter. “Together we are stronger.” The service was attended by the heads of the largest Orthodox and Catholic churches in Ukraine and the head of the Polish Bishop’s Conference, Archbishop Stanislaw Gadecki.

The Ukrainian president’s chief of staff, Andriy Yermak, wrote on Telegram that Ukraine and Poland were “united against a common enemy who dreamed of dividing us”. Duda called the service “a testimony of friendship in the face of a difficult history”.