Police and supporters of captured war crimes suspect Radovan Karadzic have clashed after a pro-nationalist march in Belgrade.
Police fired tear gas and rubber bullets to break up gangs of mostly young protesters who had gathered in the city centre.
Rioters threw rocks and fireworks at security forces, with around 45 people reportedly being treated for light injuries – 25 of them policemen.
Fighting broke out after people gathered in support of Karadzic, who was arrested on suspicion of genocide and crimes against humanity last week after more than a decade on the run.
The Serbian Radical Party bussed in thousands of protesters from all over Serbia and Bosnia. They came to show support for a man they still consider a hero for his role during the 1992-95 Bosnian war.
Both Karadzic and his military chief Ratko Mladic are indicted for the massacre at Srebrenica and the siege of Sarajevo, where more than 11,000 people died.
The extradition of Karadzic to the UN war crimes tribunal seen as key to Serbia’s closer ties with the European Union.
Belgrade will also be keen to avoid further protests and unrest with pro-nationalist supporters.