(JTA) — The World Jewish Congress urged Ukrainian clergy to refrain from attending neo-Nazi events.

“Moral authority” is necessary to “prevent any further rehabilitation of Nazism or the SS,” World Jewish Congress President Ronald Lauder wrote in a letter Thursday to the head of the Ukrainian Orthodox Church, Patriarch Filaret.

In his letter, Lauder referenced a recent ceremony near Lviv marking the 70th anniversary of the creation of the Galician division of the Waffen SS, in which Ukrainians fought on the side of Nazi Germany.

“I was horrified to see photographs … of young Ukrainians wearing the dreaded SS uniform with swastikas clearly visible on their helmets as they carried the caskets of members of this Nazi unit, lowered them into their new graves, and fired gun salutes in their honor,” Lauder wrote. “I was especially troubled by the participation in this ceremony of a priest of the Ukrainian Orthodox Church that appeared to give a religious legitimacy to the rehabilitation of the SS.”

In late July, Ukrainians wearing SS uniforms were photographed trudging through trenches and firing rifles in a reconstruction of a key battle against the Soviets during World War II. An Orthodox priest led a ceremony for fallen soldiers of the Nazi unit, sprinkling his blessing over several men sporting swastikas who lowered a coffin in a ritual reburial.

Lauder asked the Ukrainian priest to “call on the clergy of your Church not to participate in any future ceremonies or events that glorify or legitimize a uniform that epitomizes the evil of genocide.”

Some 800,000 Jews were murdered during the Holocaust in what is now Ukrainian territory, according to researchers from the University of Toronto. They were killed by German troops and Ukrainian auxiliaries who gathered the Jews, guarded them, and in many instances participated in their killing, according to the Yad Vashem Holocaust museum in Jerusalem.

Oleg Pankevich, a lawmaker for the extreme-right Svoboda party, also took part in the reburial ceremony, Lauder said.

He said that the World Jewish Congress would hold a meeting of its executive committee in Kiev next year and invited Patriarch Filaret to attend the gathering.