BELGRADE, Serbia -- Serb ultranationalists crowded a main square Tuesday night to protest the government's plan to extradite former Bosnian Serb leader Radovan Karadzic to the U.N. war crimes tribunal, while a few hundred extremists clashed with riot police.
While most of the 15,000 demonstrators sang nationalist songs and waved posters of their "Serb Hero," some hard-liners broke away from the gathering and threw rocks and burning flares at police in downtown Belgrade.
Later, police fired tear gas at large groups of protesters while pushing them from the square after the rally. Police blocked off several neighborhoods, stopping traffic and the passage of the demonstrators.
Belgrade's emergency clinic reported 46 people injured, including 25 policemen and 21 civilians. Most were lightly injured, doctors said, adding that only one civilian and one policeman were hospitalized.
Police chief Milorad Veljovic said the area was "under control" by midnight.
Riot police had taken up positions across the capital and heavily armed anti-terrorist troops guarded the U.S. Embassy as busloads of ultranationalists arrived from all over Serbia and Bosnia for the anti-government rally dubbed "Freedom for Serbia."
Many protesters carried banners and wore badges with Karadzic's name and picture. Some chanted slogans against President Boris Tadic and called for his death.
Still, police estimated the turnout at only 15,000 people -- far fewer than expected. The last major nationalist rally, in February after Kosovo's declaration of independence, drew 150,000 people and led to an attack on the U.S. Embassy amid a violent looting spree.
Aleksandar Vucic, leader of the Serbian Radical Party, which organized the rally, called for Tadic's government to be overthrown.
"Thank you for showing that Serbia is not dead, although it is being killed by Boris Tadic," Vucic told the crowd. "Thieves and bandits are ruling Serbia."
"We will fight for Serbia and Serbia will be free," he added, setting off thunderous applause and chants of "Uprising! Uprising!"
Karadzic spent nearly 13 years on the run before being arrested last week in Belgrade, only a few weeks after Tadic's government came to power. He is still revered by many as a wartime hero for helping to create the Bosnian Serb state.
Luka Karadzic told the crowd his brother should be tried in Serbia and not at the U.N. war crimes tribunal in The Hague, Netherlands.
"It is still not too late to prevent Karadzic's extradition to The Hague," he said.
Tuesday's protest was seen a test for Tadic's government, which is much more pro-Western than its predecessor. The president warned the right-wing extremists to remain peaceful.
"Everyone has the right to demonstrate, but they should know that law and order will be respected," Tadic said.
The U.S. Embassy had predicted that up to 100,000 protesters could show up and advised Americans to avoid downtown Belgrade. The embassy was heavily guarded during the rally by special troops armed with machine guns wearing masks.
After February's mass rally, the U.S. Embassy was partly burned and protesters went on a looting spree, smashing shops and McDonald's restaurants. Those protesters were angry that the U.S. had recognized Kosovo, a former province of Serbia, as an independent country.
Karadzic faces 11 charges at the U.N. tribunal, including genocide and conspiracy to commit genocide. He is accused of masterminding the 1995 slaughter of 8,000 Muslim men and boys in Srebrenica and the more than three-year siege of Sarajevo that left 10,000 people dead.
It remained unclear Tuesday whether Karadzic's lawyer had actually filed an appeal against his extradition to the U.N. tribunal.
"We have not received the appeal," a spokeswoman for Serbia's war crimes court, Ivana Ramic, said at the end of court hours Tuesday.
Karadzic's lawyer claimed he sent the appeal by registered mail before a midnight Friday deadline. But the postal service said it did not have the letter and Ramic said the court didn't either.
Under Serbian law, if an appeal was not filed or did not arrive, the court's investigative judge could rule to extradite Karadzic to U.N. tribunal without considering Karadzic's objection.
In a sign that Karadzic anticipated a quick handover to the U.N. tribunal, his nephew Dragan Karadzic was seen Tuesday delivering two large suitcases to the Belgrade prison for his uncle.
Serbia's new, pro-Western government hopes Karadzic's arrest will strengthen the country's bid for membership in the European Union. Serbia had been accused of not searching for war crimes fugitives sought by the U.N. tribunal.