Ratko Mladic has appeared in a Serbian court hours after being arrested following 16 years on the run.
Authorities want to extradite the former Bosnian Serb army chief to the war crimes tribunal in The Hague.
He faces accusations including a genocide charge over the killing of about 7,500 Bosnian Muslim men and boys at Srebrenica in 1995.
The hearing was halted pending a medical examination, his lawyers said. Court officials believe he will appeal.
The whole process is expected to take a week.
Following the arrest of Radovan Karadzic in 2008, Gen Mladic became the most prominent Bosnian war crimes suspect at large.
Serbia had been under intense international pressure to arrest him and send him to the UN International Criminal Tribunal to the former Yugoslavia in The Hague.
Serbian TV showed footage of Gen Mladic wearing a baseball cap and walking slowly as he appeared in court in Belgrade.
His lawyer, Milos Saljic, told reporters the judge had attempted to question Gen Mladic but the suspect was in a "difficult psychological and physical condition", and was unable to communicate.
The hearing is expected to be resumed on Friday, reports say.
Gen Mladic asserts that he does not recognise the authority of the UN war-crimes tribunal, Mr Saljic added.
The BBC's Mark Lowen in Belgrade says the Serbian government will be keen for Gen Mladic to be extradited quickly, hoping that his departure might prevent further protests by Serb nationalists who still see him as a defender of the Serbian people.
President Boris Tadic said Gen Mladic's arrest on Thursday had brought Serbia and the region closer to reconciliation, and opened the doors to European Union membership.
Mr Tadic rejected criticism that Serbia had been reluctant to seize Gen Mladic.
"We have been co-operating with the Hague tribunal fully from the beginning of the mandate of this government," he said.
A spokeswoman for families of Srebrenica victims, Hajra Catic, told AFP news agency: "After 16 years of waiting, for us, the victims' families, this is a relief."
Gen Mladic, 69, was seized in the province of Vojvodina in the early hours of Thursday, Serbian Justice Minister Slobodan Homan told the BBC.
Serbian security sources told AFP news agency that three special units had descended on a house in the village of Lazarevo, about 80km (50 miles) north of Belgrade.
The house was owned by a relative of Gen Mladic and had been under surveillance for the past two weeks, one of the sources added.
Reports that Gen Mladic had been living under the assumed name Milorad Komodic were denied by Serbian Interior Minister Ivica Dacic.
"It is not true that he used another identity, or that he possessed a document with someone else's name," said Mr Dacic.
Serbian media say he did not resist arrest, and was not in disguise - unlike Mr Karadzic, who had a long beard and a ponytail when he was captured in Belgrade three years ago.
Gen Mladic was indicted by the UN war crimes tribunal in The Hague in 1995 for genocide over the killings that July at Srebrenica - the worst single atrocity in Europe since World War II - and other alleged crimes.
Having lived freely in the Serbian capital, Belgrade, he disappeared after the arrest of former Yugoslav President Slobodan Milosevic in 2001.
In a message from his UN cell in the Hague, Mr Karadzic said he was sorry Gen Mladic has been arrested.
The wartime Bosnian Serb leader added that he wanted to work with him "to bring out the truth" about the Bosnian war, in a message relayed to the Associated Press news agency by his lawyer.
The arrest was hailed internationally.
UN war crimes chief prosecutor Serge Brammertz thanked the Serbian authorities for "meeting their obligations towards the tribunal and towards justice".