Serbian Justice Minister Snezana Malovic said here on Tuesday that the process to extradite Ratko Mladic to the UN war crimes tribunal has started, and that Mladic is already on a plane to The Hague.

"He is on the plane, on the way to The Hague," said the minister.

Mladic, a fugitive long wanted by the International Criminal Tribunal for the former Yugoslavia (ICTY) for alleged crimes against humanity and genocide, was escorted to the Belgrade airport earlier on Tuesday under heavy security.

Two convoys of jeeps and police cars, with sirens screaming, sped through Belgrade in the direction of the airport after leaving the premises of the Special Court, witnesses said.

According to Milos Saljic, Mladic's lawyer, a three-member chamber of the Special Court rejected an appeal against the extradition for medical reasons.

Mladic's arrest and possible extradition sparked a violent clash between protesters and police during a rally on Sunday in Belgrade.

According to a report by Radio Television Republika Srpska ( RTRS), an estimated 10,000 people on Tuesday also held a rally in support of Mladic in the central square of the Bosnian Serb capital, Banja Luka.

"Serbs have always defended what was ours," Pantelija Curguz, president of the War Veterans Association of Republika Srpska, was quoted as saying. Curguz called on the government of Republika Srpska, the Serb-dominated entity of Bosnia and Herzegovina (BiH), to provide the funds for Mladic's legal defense.

Mladic, the former commander of the Bosnian Serb Army who had been in hiding since 1996, was arrested on Thursday. He was the most high-profile fugitive still at large, dating back to the civil conflicts that erupted during the breakup of the former Yugoslavia in the 1990s.