"During the concert... many of those in attendance showed up with Ustashe uniforms, symbols and banners. This should come as no surprise, for he is the same person who expressed nostalgia in a song for two infamous Croatian concentration camps in which tens of thousands of innocent Serbs, Jews, Gypsies and anti-fascist Croatians were murdered by the Ustashe," the rabbi said in the letter.
"We understand that today Croatia is a democracy, but it is clear that this kind of behaviour left unanswered will not only mock the victims of the past but threaten the future of democracy," the letter read.
The rabbi forwarded the letter also to House Committee on Foreign Affairs chairman Tom Lantos, Senate Committee on Foreign Relations chairman Joe Biden, and Senator Dianne Feinstein.
He also called for revising the new exhibition at the museum in Jasenovac. The exhibit should "name the criminals" and explain that "it was Ustashe's racism, antisemitism and xenophobia that spawned Jasenovac" so that "young Croatians will fully understand the horrors of the past".
Rabbi Cooper also called for taking the necessary legislative steps to ban the use of Ustashe symbols in Croatia the way the swastika was banned in Germany and Austria.
Ambassador Jurica told Hina he had sent a reply to Cooper "which is in accordance with the positions taken on this issue by the Croatian government".
In a reaction to events at the concert and protests from Jewish associations in Croatia and abroad, in a June 19 statement the government rejected attempts to use and display insignia and salutes from the WWII Ustashe regime, underlining that present-day Croatia rested on the values of antifascism and calling on all, notably those with influence over young people, to promote European values.
Jurica said he additionally informed Cooper about the new exhibition at Jasenovac, saying it had been prepared in cooperation with experts from the Yad Vashem Museum in Israel and the Holocaust Museum in Washington.