WARSAW, Poland — Hundreds of Poles prayed Sunday for victims of World War II-era massacres by Ukrainians before an anniversary that remains a sore point between the neighboring nations.

Tens of thousands of ethnic Poles, including men, women and children, were killed or hacked to death and their villages burned down during 1943 and 1944 in what was then Nazi-occupied eastern Poland and is now western Ukraine. Poles are marking the July 11, 1943 anniversary, the day of the worst bloodshed, in which Ukrainian nationalists attacked 100 villages. Their plan was to have a sovereign and nationally homogenous Ukraine after the war. Sometimes, their action was met with retaliation.

The painful past is a sore point in otherwise friendly relations between Poland and Ukraine.

After much debate, Poland's Senate, in a recent statement marking the anniversary, toned down the use of the word "genocide," to describe the killing, a term used in Poland but rejected by Ukraine.

"The organized and massive nature of these crimes and the accompanying cruelty mark them as ethnic cleansing that bears signs of genocide," the senators said.

At a recent meeting, national church leaders offered apologies and appealed for forgiveness and reconciliation.

"We know that the Christian assessment of the crimes in Wolyn (region) is calling for our unequivocal condemnations and apology," Polish and Ukrainian church Ieaders said in a joint declaration.

Still, Ukrainian President Viktor Yanukovych has declined to go to religious observances next weekend in Ukraine, which his Polish counterpart, Bronislaw Komorowski, plans to attend. The Ukrainians also say the killings were provoked by anti-Ukraine Polish partisans.

Under communism, talk about the killings was taboo and historians are only now revealing the details. With evidence basing chiefly on survivor accounts, historians estimate Polish victims at around 60,000 and Ukrainian victims at up to 20,000.

Families who once lived in the area prayed Sunday at Poland's Jasna Gora shrine in the southern city of Czestochowa.

In his homily, the outspoken Rev. Tadeusz Isakowicz Zaleski insisted on the genocide term.

"Euphemisms are used: 'the Wolyn tragedy, ethnic cleansing.' You can clean your clothes, when they are dirty, but to kill women, children and old people does not amount to cleansing, it amounts to genocide."

Documents recently uncovered by The Associated Press show that Michael Karkoc, who was a commander of a Nazi SS-led Ukrainian unit that is accused of taking part in at least one massacre of a Polish village in 1944, is living in the United States, after he allegedly lied about his wartime past to the authorities to be let into the country. No records uncovered by the AP indicate Karkoc had a direct link to the killings.