Protesters have clashed with riot police in Belgrade after several thousand Serbian nationalist supporters of jailed war-crimes suspect Ratko Mladic rallied to demand his release.
More than 100 people were arrested after rioters overturned bins, broke traffic lights and set off firecrackers in the city centre on Sunday night.
Doctors said six police officers were among 16 people taken to hospital with injuries.
The clashes began after a rally that drew at least 7,000 demonstrators, many singing nationalist songs and carrying banners honouring Mladic, the former Bosnian Serb military commander.
The protest came hours before an expected appeal by the legal team for the alleged war criminal to appeal extradition to the UN war crimes court in The Hague, Netherlands.
Some chanted right-wing slogans and a few gave Nazi salutes, and supporters of the extreme nationalist Serbian Radical Party were bussed in to attend the rally.
Right-wing extremists and hooligan groups also urged followers to appear in large numbers, creating the biggest test of Serbian sentiment and the government's resolve since Mladic's arrest last Thursday.
The demonstrators, who consider Mladic a hero, said Serbia should not hand him over to the war crimes court.
"Cooperation with The Hague tribunal represents treason," Radical Party official Lidija Vukicevic told the crowd.
"This is a protest against the shameful arrest of the Serbian hero."
Demonstrators demanded the ousting of Serbian President Boris Tadic, who ordered Mladic's arrest. A sign on the stage read, "Tadic is not Serbia."
More than 3,000 riot police were deployed around government buildings and Western embassies, and riot police tried to block small groups of extremists from reaching the rally.
Nationalists are furious that the Serbian government apprehended Mladic, 69, after nearly 16 years on the run, at a relative's home in a northern Serbian village.
Mladic stands accused of masterminding the 44-month siege of Sarajevo and the 1995 massacre of 8,000 Muslim men and boys in Srebrenica.
His arrest is considered critical to Serbia's efforts to join the European Union, and for reconciliation in the region after a series of ethnic wars of the 1990s.
Some 3,000 supporters also arrived by bus from other parts of Bosnia to a rally at Kalinovik on Sunday, the area where Mladic grew up.
Many wore black T-shirts with Mladic's picture and the words "Serbia in my heart" and said they would fight under Mladic again.
The Kalinovik protesters headed afterward to the shack Mladic was born in at the end of a steep, muddy road in the village of Bozanici, turning the shabby house into a pilgrimage site where his relatives addressed the crowd.
Mladic's family and lawyers have been fighting his extradition, arguing the former general is too ill to face charges.
However, a judge ruled on Friday the former Bosnian Serb military general could be extradited to The Netherlands.
The family plans to appeal the extradition and to demand an independent medical check-up - moves described by the authorities as a delaying tactics.
His lawyer Milos Saljic said that Mladic above all keeps demanding that he be allowed to visit the grave of his daughter, who committed suicide in 1994.
"He says if he can't go there, he wants his daughter's coffin brought in here," the lawyer said. He added: "His condition is alarming."