Warsaw, Poland—— Ukrainian President Volodymyr Zelensky visited Poland on Wednesday after the two countries reached an agreement on a source of long-running tensions between the two countries: the exhumation of Polish victims of World War II-era massacres by Ukrainian nationalists.

Polish Prime Minister Donald Tusk's office said earlier on Wednesday that he would welcome Zelenskiy later in the morning and the two would hold a joint news conference shortly after noon local time.

The visit comes days after Tusk announced progress on the exhumation issue, an issue that has strained relations between the two countries for years.

“Finally there has been a breakthrough. A decision has been made regarding the first exhumation of Polish victims of the UPA,” Tusk wrote on social platform Good cooperation. We are awaiting further decisions. "

The NGO Foundation for Freedom and Democracy said on Monday it would begin exhuming Ukrainian victims in April.

Although Poland has been one of Ukraine's staunchest supporters since Russia's full-scale invasion nearly three years ago, the fact that Polish victims still lie in mass graves on Ukrainian soil eight years after they were killed has raised concerns among many It left a legacy of growing suffering among the Poles.

It also puts pressure on Tusk, who is seeking to make progress on an issue that remains important to many in Poland. This is particularly important as his party's candidates are expected to face a strong challenge from nationalist opposition candidates in May's presidential election.

The problem dates back to 1943-44, when Europe was at war. Ukrainian nationalists massacred approximately 100,000 Poles in Volhynia and other areas of eastern Poland that were under Nazi German occupation and are now part of Ukraine.

Entire villages were burned and residents murdered by nationalists and their associates seeking to establish an independent Ukrainian state. Poland considers the events to be genocide and has been asking Ukraine to allow them to exhume the victims and provide them with proper burials.

An estimated 15,000 Ukrainians were killed in retaliation.

The issue is difficult for Ukraine because some World War II-era Ukrainian nationalists are considered national heroes for their fight for Ukrainian statehood.

As the two sides moved to resolve the issue, the Speaker of the Ukrainian Parliament made conciliatory remarks in the Polish Parliament in May 2023.

"Human life has equal value regardless of nationality, race, gender or religion," Ruslan Stefanchuk told Polish lawmakers at the time. "With this understanding, we will cooperate with you, dear Polish friends, and we will accept the truth, no matter how uncompromising it may be."