Former Bosnian Serb leader Radovan Karadzic is being extradited to the United Nations' war crimes tribunal in The Hague, officials announced Wednesday.

The Serbian government said in a statement issued early Wednesday that its justice ministry had issued a decree permitting Karadzic's handover.

In the Netherlands, Dutch and UN officials prepared to receive him, clearing the courtyard at a jail near The Hague where he is expected to be held.

Upon Karadzic's arrival, officials will perform an identity check as well as a medical test on him.

News of Karadzic's extradition came early Wednesday morning when an official at the Serb war crimes prosecutor's office, who spoke on condition of anonymity, told the Associated Press that Karadzic was in one of three jeeps with tinted windows seen leaving the Belgrade war crimes court at 3:45 a.m. local time Wednesday.

The official said the jeeps were on their way to Belgrade airport, where Karadzic was to depart for the Netherlands. A business jet that was believed to be transporting Karadzic was seen taking off about 15 minutes later.

Protesters clash with police in central Belgrade on Tuesday following an anti-government rally in support of Bosnian Serb war crimes suspect Radovan Karadzic. (Srdjan Ilic/Associated Press)

The extradition came as a surprise after a Belgrade court hearing Karadzic's appeal of his extradition to the UN tribunal still hadn't received appeal documents by the close of business Tuesday, meaning a panel of three judges could not rule on the case and that Karadzic would remain in the Serbian capital for the time being.

Under Serbian law, an appellant only has to show that the appeal had been mailed before the deadline, potentially from anywhere in the world.

But if an appeal is not filed, or if it is sent by mail but doesn't arrive, the court's investigative judge could rule to extradite Karadzic without considering his objection.

Karadzic was arrested last week on an international genocide indictment. His lawyer, Svetozar Vujacic, said Monday he was attempting to delay Karadzic's appeal process by mailing the appeal documents at the last possible minute, in order to keep his client in Belgrade as long as possible.

"The law is not specific on how long the court should wait," Vujacic said. "It is also not written in the law where the appeal may be sent from. Widely interpreted, it could be from Sydney, although of course I did not actually send it from Sydney."

Thousands rally in support of Karadzic

The announcement of Karadzic's extradition followed a nationalist rally, attended by thousands of Serbian hardliners who support Karadzic and are against the country's pro-Western government, that turned violent Tuesday.

"The demonstration tonight sort of broke up and then suddenly turned violent," Neil MacDonald, a reporter for the Financial Times, told CBC News from Belgrade.

"A few groups of young protesters started ... throwing stones at police. Police responded with tear gas, and what was meant to be a kind of relatively orderly march through the city disintegrated into a lot of people running around in different directions and protesters throwing things at police and police responding by beating some of the protesters."

Belgrade's emergency clinic reported 46 people were injured, including 25 policemen and 21 civilians, but doctors said no one appeared to have life-threatening wounds. Police estimated 15,000 people attended the rally.

Many Serbian extremists still regard Karadzic as a hero for helping to create a Serb ministate in Bosnia during the 1992-95 Balkan war.

Karadzic, 63, is accused of masterminding Europe's worst massacre since the Second World War, the killing in 1995 of 8,000 Muslim men and boys in Srebrenica, Bosnia, as part of a genocidal campaign to make Bosnia a Serb-only country.

The 11 charges against Karadzic at the UN tribunal, relating to the Srebrenica massacre, include genocide, war crimes, crimes against humanity and other atrocities.

Test case for new government

In many ways, Tuesday's protests are a test case for Serbian President Boris Tadic's government, which is more closely allied with the West than its predecessors. The new Serbian president has received death threats from the radicals following Karadzic's arrest.

"Everyone has the right to demonstrate, but they should know that law and order will be respected," Tadic cautioned Tuesday.

The last time Serbian ultranationalists organized a mass rally in February, the U.S. Embassy was partly burned and protesters went on a looting spree in Belgrade. Protesters, numbering about 150,000, were angry that the United States had recognized Kosovo, a former region in Serbia, as an independent country.

Tadic's government also hopes Karadzic's arrest will strengthen the country's bid for European Union membership.

Responding to the capture of Karadzic, the EU on Tuesday voted to delay a decision on whether to open up special trade benefits to Serbia. The 27-member bloc has been pressuring Tadic's government to co-operate on war-crimes prosecutions related to the Balkan war, and following Karadzic's arrest enlargement commissioner Olli Rehn urged the EU to grant Serbia better trade conditions.

EU ambassadors said they were waiting for the handover of Karadzic to the UN tribunal in The Hague and for a report from the tribunal's prosecutor as to whether Serbia was co-operating.

With files from the Associated Press