Radovan Karadzic has arrived in the Netherlands, where the former Bosnian Serb leader will be put on trial in The Hague for alleged crimes against humanity.

The BBC reports that Karadzic is now in the detention centre of the United Nations court.

He reportedly arrived at the Rotterdam airport around dawn, shortly after the Serb war crimes prosecutor's office announced his extradition was underway.

Just hours earlier, police fired rubber bullets at several hundred extremists at a pro-Karadzic rally in Belgrade, where at least 15,000 people protested the decision to remove him from the country.

Video footage showed police trying to control a group of ultranationalists at the edges of the rally. Police fired tear gas canisters into the mob and tried to force them back.

More than two dozen people suffered non-life-threatening injuries, including a Spanish television journalist, officials told The Associated Press.

Karadzic, the wartime leader of the Bosnian Serbs, is facing 11 charges, including genocide and crimes against humanity for allegedly leading ethnic cleansing campaigns against Croats and Muslims in the 1992-1995 Bosnian war.

At Tuesday's rally, protesters sang songs for Karadzic and called on the government to allow him to defend the charges in a Serbian court.

"This rally will be a symbol of resistance, a symbol of the strength of those who love freedom more than anything," Aleksandar Vucic of the nationalist Radical Party told Reuters.

"We'll continue resisting dictatorship in Serbia, we'll continue raising the question of whose paramilitary forces arrested Radovan Karadzic, how and why."

Officials had been debating whether to extradite Karadzic before or after the rally.

Some officials were concerned protesters would use the extradition as "an excuse to turn violent," CNN`s Alessio Vinci told CTV's Canada AM on Tuesday.

However, other officials feared the courthouse where Karadzic is being held would be targeted by protesters.

Despite the violence, only a small number appear to have engaged the police. Radio Free Europe's Zoran Glavonjic told CTV Newsnet there were enough police to deal with any disruptions.

Karadzic, a psychiatrist-turned-Serbian-nationalist, is accused of masterminding the deadly wartime siege of Sarajevo and the 1995 executions of about 8,000 Muslim boys and men in Srebrenica.

Karadzic eluded authorities for 13 years by hiding in plain sight -- he grew a beard, worked in an alternative medicine clinic, and even gave lectures and had his own website.

The former Bosnian Serb president was arrested July 21 in a Belgrade suburb.

With files from The Associated Press