JASENOVAC, Croatia — Visiting ecumenical Patriarch Bartholomew I, considered the spiritual head of Orthodox church leaders, on Saturday commemorated the victims of Croatia’s most notorious World War II death camp.

Bartholomew I, the Patriarch of Constantinople based in Istanbul, in the first visit by the spiritual leader of the Orthodox Church to the country, presided over a mass in the church at Jasenovac and visited the site of the camp known as “Croatia’s Auschwitz.”

The camp, whose site is now home to a memorial, was set up in mid-1941 by the pro-Nazi regime and dismantled in 1945. Croatia’s WWII pro-Nazi Ustasha regime persecuted and killed ethnic Serbs, who are mostly Orthodox Christians, Jews, Romas and anti-fascist Croatians.

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The total number of people killed at Jasenovac, some 60 miles southeast of the capital Zagreb, remains disputed. It varies from tens of thousands to 700,000, according to Serbian figures.

Bartholomew, who arrived for a two-day visit to Croatia on Friday, was accompanied by Croatian Serb leader Milorad Pupovac, as well as Orthodox church dignitaries from Serbia, Bosnia, Montenegro and Croatia.

Pupovac earlier hailed the visit stressing the Patriarch was a “man who has been encouraging a dialogue also at a time where there was not much dialogue between Catholics and Orthodox, notably in Croatia.”

Nearly 90 percent of Croatia’s population of 4.2 million are Roman Catholics. Orthodox ethnic Serbs are the country’s largest minority making up four percent of the population.

Ties with ethnic Serbs and Serbia remain strained since Croatia’s 1990s war of independence during which Belgrade backed rebel Serbs.

In recent months ties have sunk to their lowest level since the conflict. The two countries have been exchanging bitter accusations over their wartime past, with Belgrade accusing Zagreb of a “rebirth of Nazism” in reference to a far-right surge under conservative rulers.

Due to Croatia’s shift to the right ethnic Serbs, Jews and anti-fascists this year boycotted an official memorial ceremony at Jasenovac.