The Nazi-hunting Simon Wiesenthal Center said Wednesday it has lodged a formal complaint with Austrian authorities over what it termed their "utter failure" to prevent the use of Nazi-era symbols during a weekend gathering of Croatian nationalists. Efraim Zuroff, the group's Israel director, said the center filed a protest with Austria's embassy in Jerusalem alleging that officials failed to stop the display of symbols at a Sunday rally in the southern Austrian town of Bleiburg to remember victims of the post-World War II killings there. Up to 40,000 people, some of them troops loyal to pro-Nazi dictator Ante Pavelic but most civilians, who fled Croatia as it was being liberated by anti-fascist forces, were killed by vengeful Yugoslav soldiers in Bleiburg at the end of World War II. The annual rally is attended by Croatian government officials, but also attracts die-hard nationalists. "The fascist demonstrators at Bleiburg made a mockery of Austria's ban on the use of Nazi symbols and its law against Holocaust denial," Zuroff said in a statement.