Officials say the war crimes suspect had spent over a decade on the run living under the assumed identity of a health guru and heavily disguised with long white beard and hair as well as large glasses.
Late on Tuesday, Serb nationalists protesting against plans to extradite Karadzic clashed with police in Belgrade.
|Protesters fought street battles with government forces late on Tuesday [AFP]
Dozens of protesters fought running battles with police in the streets of the Serbian capital late on Tuesday, after 15,000 people turned out for a rally in support of the former Bosnian Serb leader.
Rioters threw stones, firecrackers and flaming bottles at police, who responded with tear gas and rubber bullets.
Belgrade's emergency clinic reported that 46 people were injured, including 25 policemen, most of them with light injuries.
Al Jazeera's Alan Fisher, reporting from Belgrade, said the violence erupted as the rally was coming to a close.
The Serbian Radical party, which had organised the rally, said it had brought in Karadzic supporters by bus from all over Serbia and Bosnia, where Karadzic is still revered by many as a wartime hero.