Del Ponte told the Belgrade government that Mladic, allegedly involved in killing 8,000 Bosnian Muslims, should be surrendered, the BBC reported. The massacre of men and boys at Srebenica in July 1995 was the worst atrocity in Europe since World War II.
"Mladic is in Serbia, and, as you know, Mladic is protected with power of the army," del Ponte said.
European Union Enlargement Commissioner Olli Rehn said that Serbia's unwillingness to hand over wanted war criminals could be a deal-breaker in its efforts to join the EU.
"Serbia has to choose now between the nationalist past and a European future," he said. "I hope they choose the European future."