The search is taking place in the former village of Huta Pieniacka—now Huta Peniatska in Ukraine's Lviv region—where hundreds of ethnic Poles were killed in February 1944.
The work is being carried out by Poland's Institute of National Remembrance (IPN) in cooperation with Ukrainian partners.
"We are looking for at least two mass burial pits," Tomasz Trzaska of the IPN's Office for Search and Identification told Poland's PAP news agency.
He said the suspected burial sites had been preliminarily identified based on witness testimonies, historical photographs and the area's topography.
Excavations are focused on land surrounding a former chapel and church that no longer exist.
A small excavator has begun removing topsoil so archaeologists can examine the site for evidence of graves, the PAP news agency reported.
According to Trzaska, the IPN has identified 634 victims by name but estimates that between 800 and 1,000 people may have been killed in the massacre.
The higher estimate reflects the presence of refugees from nearby villages who had sought shelter in Huta Pieniacka, he said.
Under Ukrainian regulations, exhumations can begin only after burial sites have been formally located.
The search is scheduled to continue through June 19. Representatives from Poland's culture ministry and an association of descendants of Huta Pieniacka residents are also participating.
Historians say that on February 28, 1944, Polish residents of Huta Pieniacka were killed by a unit of the 14th Waffen-SS Galizien Division, operating under German command, with the participation of Ukrainian nationalist forces.
According to findings by Polish prosecutors, about 850 people were killed and the village was destroyed.
The killings were among a series of massacres known in Poland as the Volhynia massacres.
Polish historians estimate that about 100,000 Poles were killed by the Ukrainian Insurgent Army (UPA) and associated nationalist formations between 1943 and 1945 in what was then German-occupied eastern Poland and is now western Ukraine.
The legacy of the wartime violence remains a sensitive issue in relations between Poland and Ukraine, with differing interpretations of the role of the Organisation of Ukrainian Nationalists (OUN) and the UPA.
Poland regards the killings as genocide, while many in Ukraine view the violence as part of a broader wartime conflict involving both sides and emphasize the groups' later resistance to Soviet rule.
Volhynia, which was part of prewar Poland, was occupied by the Soviet Union in 1939 and by Nazi Germany in 1941.
Efforts to locate and exhume Polish victims in Ukraine were suspended for years after Ukrainian authorities imposed a moratorium in 2017 following the dismantling of a UPA monument in southeastern Poland.
The ban was lifted in late 2024, when the foreign ministers of Poland and Ukraine announced an agreement allowing search and exhumation work to resume in accordance with Ukrainian law.
Earlier this year, investigators conducted exhumations at the former Polish village of Puźniki, now Puzhnyky in western Ukraine, where the remains of at least 42 victims were recovered.
Additional burial sites have been identified in the former villages of Ostrówki and Wola Ostrowiecka in the Volhynia region.
Ukraine's cultureministry last week approved exhumation work at those locations, while further searches and excavations are planned at Huta Pieniacka and other sites linked to the wartime massacres.
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Source: IAR, PAP