Police fired tear gas to break up scuffles with youths during a demonstration by hardline Serbian nationalists in support of war crimes suspect Radovan Karadzic on Tuesday.
Karadzic's legal team meanwhile worked on its campaign to block the former Bosnian Serb leader's extradition to an international tribunal to answer charges of genocide for his actions in the 1992-95 Bosnia war. He was arrested last week in Serbia after 11 years on the run, most recently living under an assumed name as a bearded, long-haired alternative healer. He is now in a Belgrade prison awaiting transfer to the United Nations war crimes tribunal in The Hague.
Hardliners see him as a hero and defender of the Serb nation. Some 10,000 people, many bussed in from rural nationalist strongholds, gathered in downtown Belgrade for an evening rally to show their support for him.
Clashes broke out when several dozen youths linked to hooligan groups threw flares, stones and garbage cans at riot police. Security forces responded with baton charges and rounds of tear gas.
Serbian media said about 20 people were treated for light injuries in Belgrade hospitals, half of them policemen. "I came in Belgrade to protest against Karadzic's extradition," said 60-year-old Slobodanka Sanojevic, speaking before the unrest. "He is a great man, he created a state for Serbs (in Bosnia) and saved Serbian children from genocide."
Karadzic, with his military chief Ratko Mladic, is indicted for the massacre of 8,000 Bosnian Muslims at Srebrenica and the 43-month siege of Sarajevo, where more than 11,000 people died from shelling, sniper fire, malnutrition and illness.
His delivery to The Hague is key to Serbia's closer ties with the European Union and his arrest was seen as a clear pro-Western signal by the new government, sworn in earlier this month.