(JTA) — A senior state historian of Ukraine accused Israel’s president of repeating a Soviet “myth” about Ukrainians’ complicity in the Holocaust as the East European country held the largest event in its history commemorating the genocide.

Volodymyr Vyatorovych, director of the Ukrainian Institute of National Remembrance, leveled the accusation against Reuven Rivlin Friday, as hundreds of guests from dozens of countries were preparing to convene at Babi Yar for a ceremony to commemorate the murder 75 years ago of at least 33,000 Jews at that ravine in Kiev.

The Ukrainian government organized the event in cooperation with the World Jewish Congress.

Rivlin, who is scheduled to attend the ceremony, said during his speech Wednesday before the Ukrainian parliament that members of the nationalist OUN militia and others were complicit in the Nazi extermination of Jews in Ukraine. This prompted Vyatorovych to say that Rivlin “repeated the Soviet myth” of involvement by the OUN militia, Ria Novosti Ukraina on Friday reported.

The exchange comes amid a polarizing debate about the Holocaust in Ukraine, where in 2014 nationalists led a successful revolution against a president whom they said was a pawn of Russia. Many Ukrainians perceive Moscow as an enemy out to deny sovereignty to their nation.

Rising nationalism in post-revolution Ukraine, critics have charged, is leading to the veneration of war criminals who murdered Jews alongside the Nazis and their celebration as patriotic heroes because they also fought against Russian domination.

In a rare joint statement, more than 20 Ukrainian Jewish groups in July called such moves a form of “Holocaust denial.” Eduard Dolinsky, director of the Ukrainian Jewish Committee, said they were undermining the sincerity of the government’s efforts to commemorate the Babi Yar anniversary, and overshadowing the event.

Acknowledging these concerns, Rivlin said during his speech: “About half a million Jews were murdered in what is now Ukraine during World War II, in Babi Yar and many other places, they were shot in Forests or in ravines. Many collaborations in these crises were Ukrainians. Among them, combatants of the OUN stand out especially [for how] they humiliated Jews, killed them, and in many cases betrayed them to the Germans.”

Rivlin’s statement caused an uproar among nationalist politicians and other key figures in Ukraine. Bogdan Chervak, the first deputy chairman on the State Committee for Television and Radio of Ukraine, said that “What Rivlin did can unambiguously be interpreted as sitting in the face of Ukrainians” at a time when the people he accused of perpetrating crimes are no longer alive to defend themselves.

Rivlin also noted the actions of Ukrainian non-Jews who risked their lives to save Jews during the Holocaust. Israel’s Holocaust commemoration authority, Yad Vashem, has awarded 2,544 Ukrainians with the title of Righteous among the Nations for such actions. Ukraine has the fourth largest number of Righteous, after Poland, the Netherlands and France.

Ukrainian President Petro Poroshenko on Friday called on the international community to financially support the creation of the Holocaust memorial museum in Babi Yar.

“I urge the Ukrainian and world community to join this initiative,” he said during the presentation of the film about the massacre.