The rally in the Serbian capital, where Karadzic is being detained, has been organised by the hardline Radical Party and backed by the party former nationalist prime minister Vojislav Kostunica, both sidelined after May 11 elections.

The Radicals hope "tens of thousands" of Karadzic loyalists from across the country will attend the protest, which comes one week after the wartime Bosnian Serb leader was captured in disguise as an alternative medicine guru.

A firebrand leader of the ultra-nationalist party, Aleksandar Vucic, said the demonstration was against Serbia's pro-Western President Boris Tadic for ordering Karadzic's arrest.

"The protest is against the treacherous and dictatorial regime" of Tadic, he said ahead of the demonstration, the first major show of force against Karadzic's arrest.

The protest is expected to be the biggest in Belgrade since February, when 150,000 protested Kosovo's declaration of independence from Serbia in a rally that sparked attacks on Western embassies, wild rioting and looting.

It is due to start at 7:00 pm (1700 GMT) in Belgrade's main Republic Square, which is much smaller than the area where the Kosovo rally was staged in front of the old Yugoslav parliament building.

Vucic has called for a peaceful march through Belgrade's central streets to show the "unity of all the free people of Serbia," while Karadzic's brother Luka has promised a "Gandhi-like" protest.

Karadzic is fighting his transfer to The Hague, where he stands accused of playing a leading role in the siege of Sarajevo and Srebrenica massacre of Muslim males, the bloodiest single atrocity in Europe since World War II.

But his lawyer Svetozar Vujacic openly admits the appeal, posted by regular mail at the latest possible moment before the weekend, is a tactic designed to delay his transfer to the International Criminal Tribunal for the former Yugoslavia (ICTY).

And the appeal was still in the post on Tuesday, according to Ivana Ramic, the spokeswoman for its intended recipients at Serbia's special war crimes court.

Once the appeal is received, a three-judge panel of the court has three days to decide on its merits before the justice ministry must issue a final order for the transfer.

Despite some reports to the contrary, Serbia is unlikely to order the transfer of Karadzic until after the protest so as to avoid the risk of it getting out of hand.

Riot police will turn out in force to avoid a repeat of that, or any attacks on journalists like those that have marred smaller daily protests that have been staged in support of Karadzic since his capture.

Karadzic, 63, was arrested on July 21 while riding a suburban bus through Belgrade, after more than a decade on the run disguised as a specialist in "human quantum energy."

He had vanished from public life in 1996, shortly after the ICTY issued an arrest warrant for him.

Whilst in hiding, he completely changed his appearance and identity, styling himself as Doctor Dragan Dabic and donning large spectacles and a white Panama atop long white hair and a bushy beard.

Serbian state television RTS showed footage of Karadzic, under his alter ego as the health guru, attending a celebration at a private health clinic on June 22.

"Good afternoon, how do you do," said Karadzic, before milling with dozens of unsuspecting participants and at times furtively turning away from the camera filming his attendance.

But in his prison cell, Karadzic cut a "calm and sad" figure, according to a report Tuesday in the newspaper Vecernje Novosti citing close family members.

To bide his time, he has asked them to provide him with several books by Serbian and Russian authors, one of Latin quotations and William Shakespeare's "sonnets."

Karadzic