Mr Karadzic reinvented himself as a devotee of alternative medicine
A lawyer acting for the former Bosnian Serb leader Radovan Karadzic has said he will fight moves to extradite him to the UN war crimes court at The Hague.
Mr Karadzic is wanted on charges of genocide and crimes against humanity.
He was arrested in Serbia on Monday, and has three days in which to appeal against his transfer to The Hague.
The Serbian Foreign Minister, Vuk Jeremic, said the arrest of Mr Karadzic showed his country was firmly committed to European Union membership.
The arrest of Mr Karadzic and other indicted war criminals is one of the main conditions of Serbian progress towards joining the EU.
A new European-leaning government took office in Serbia about two weeks ago.
"One of the utmost priorities for the Serbian government is to make sure that Serbia continues along the path towards full EU membership. There's one remaining obstacle, which is full cooperation with the Hague Tribunal... we have demonstrated that we are really determined in removing this obstacle," Mr Jeremic told the BBC.
The EU Enlargement Commissioner Olli Rehn said the arrest had moved Serbia closer to EU candidate status and should pave the way for closer trade ties.
Mr Karadzic, 63, was questioned by a Serbian judge on Tuesday, who ruled that he should be extradited. But his lawyer, Svetozar Vujacic, said he would appeal against the ruling.
"I do not think they will accept my appeal but I want to disrupt their plans to extradite him. I'll use the legal opportunity to appeal on the last possible day, which is Friday. Radovan is feeling great, he is much calmer than I am, he is healthy," he said.
Under Serbia's law on cooperation with the Hague Tribunal, three hurdles must be crossed before Mr Karadzic is sent to The Hague.
Eleven counts of genocide, war crimes, crimes against humanity and other atrocities
Charged over shelling Sarajevo during the city's siege, in which some 12,000 civilians died
Allegedly organised the massacre of up to 8,000 Bosniak men and youths in Srebrenica
Targeted Bosniak and Croat political leaders, intellectuals and professionals
Unlawfully deported and transferred civilians because of national or religious identity
Destroyed homes, businesses and sacred sites
A magistrate must conclude that all conditions for extradition have been met. Mr Karadzic must be granted a chance to appeal and a special committee of the war crimes court must rule on that appeal. The whole process could take anything from three to nine days.
The BBC's Nick Thorpe in Belgrade says the city is now alive with speculation that the last two men on the Tribunal wanted list - Mr Karadzic's former military commander Ratko Mladic, and Goran Hadzic, a former Serb politician wanted for "ethnic cleansing" in Croatia, could be next.
Serbian intelligence officers were on the trail of Ratko Mladic when they stumbled upon Mr Karadzic, said the office of Serbia's war crimes prosecutor.
But General Mladic has strong links with the Serb army and might put up more resistance than Mr Karadzic, our correspondent says.
Mr Karadzic was living in disguise in Serbia's capital Belgrade and practising alternative medicine under the name of Dragan Dabic.
He was arrested on Monday evening on a bus in a Belgrade suburb after more than a decade on the run.
Mr Karadzic has been indicted by the UN tribunal for war crimes and genocide relating to the war in Bosnia in the mid-1990s.
The UN says Mr Karadzic's forces killed up to 8,000 Bosniak men and boys from Srebrenica in July 1995 as part of a campaign to "terrorise and demoralise the Bosnian Muslim and Bosnian Croat population".
He has also been charged over the shelling of Sarajevo, and the use of 284 UN peacekeepers as human shields in May and June 1995.
Mr Karadzic has denied the charges against him and refused to recognise the legitimacy of the UN tribunal.
The chief prosecutor in The Hague, Serge Brammertz, said the arrest made clear that no-one was beyond the law. Mr Karadzic had last been seen in public in eastern Bosnia in 1996, and was previously thought to have hidden in Serb-controlled parts of Bosnia, as well as in Montenegro and Serbia.
After the accord that ended the Bosnian war was signed in late 1995 in Dayton, in the US state of Ohio, the former nationalist president went into hiding.
International pressure to catch Mr Karadzic mounted in spring 2005 when several of his former generals surrendered, and a video of Bosnian Serb soldiers shooting captives from Srebrenica shocked television viewers in former Yugoslavia.
He was a close ally of former Yugoslav President Slobodan Milosevic, who was himself extradited to The Hague tribunal in 2001, but died in 2006, shortly before a verdict was due to be delivered in his case.