BELGRADE, Serbia -- Former Bosnian Serb leader Radovan Karadzic, accused architect of massacres that had made him one of the world's top war crimes fugitives, was arrested last evening in a raid that ended a nearly 13-year manhunt, the country's president and the U.N. tribunal said.

Mr. Karadzic is the suspected mastermind of mass killings that the U.N. war crimes tribunal described as "scenes from hell, written on the darkest pages of human history." They include the 1995 massacre of 8,000 Muslims in Srebrenica, Europe's worst slaughter since World War II.

"This is a very important day for the victims who have waited for this arrest for over a decade. It is also an important day for international justice, because it clearly demonstrates that nobody is beyond the reach of the law," said Serge Brammertz, the tribunal's head prosecutor.

President Boris Tadic's office said Mr. Karadzic has been taken before the investigative judge of Serbia's war crimes court -- a legal procedure which indicates that he could soon be extradited to the U.N. court at The Hague, Netherlands.

If Mr. Karadzic is transferred there, he would be the 44th Serb suspect extradited to the tribunal. The others include former President Slobodan Milosevic, who was ousted in 2000 and died in 2006 while on trial on war crimes charges.

Heavily armed special forces have been deployed around the war crimes court in Belgrade, where Mr. Karadzic reportedly was being held. Mr. Karadzic's brother, Luka, also arrived at the site in central Belgrade.

Serbian police deployed throughout central Belgrade as well as in front of the U.S. embassy, which was targeted in February during nationalist rioting over the former province of Kosovo's declaration of independence.

The White House called the arrest "an important demonstration of the Serbian government's determination to honor its commitment to cooperate with the International Criminal Tribunal."

The former Bosnian Serb leader has topped the tribunal's most-wanted list since his indictment in July 1995, and Serbia has been under increasing international pressure to find him and turn him over.

"He was at large because the Yugoslav army was protecting him. But this guy, in my view, was worse than Milosevic," former U.N. Ambassador Richard Holbrooke, who negotiated an end to the Bosnian War, told CNN. "He was the intellectual leader."

Mr. Holbrooke calculated that Mr. Karadzic was responsible, directly or indirectly, for the deaths of 300,000 people because, without him, there would have been no war or genocide.

The charges against him, last amended in May 2000, are genocide, extermination, murder, wilful killing, deportation, inhumane acts and other crimes committed against Bosnian Muslim, Bosnian Croat and other non-Serb civilians in Bosnia and Herzegovina during the 1992-1995 war. The specific allegations include six counts of genocide and complicity in genocide, two counts of crimes against humanity as well as violating laws of war and gravely breaching the Geneva Conventions.

The indictment alleges that Mr. Karadzic, in concert with others, committed the crimes to secure control of areas of Bosnia that had been proclaimed part of the "Serbian Republic" and to reduce its non-Serb population significantly.

"These offenses include a brutal campaign of ethnic cleansing directed at non-Serbs, organized attacks on places of worship, the operation of concentration camps and the mass murder of thousands of Bosnian Muslim and Bosnian Croat civilians," the White House said in a statement.

The fugitive's wife, Ljiljana, told The Associated Press by phone from her home in Mr. Karadzic's former stronghold, Pale, near Sarajevo, that her daughter Sonja had called her before midnight. "As the phone rang, I knew something was wrong. I'm shocked, confused. At least now we know he is alive," Ljiljana Karadzic said, declining further comment.

As leader of Bosnia's Serbs, Mr. Karadzic hobnobbed with international negotiators, and his interviews were top news items during the 3 ¹/₂-year Bosnian war, set off when a government dominated by Slavic Muslims and Croats declared independence from Yugoslavia in 1992.