PARIS  Radovan Karadzic, one of the world’s most wanted war criminals for his part in the massacre of nearly 8,000 Muslim men and boys in Srebrenica in 1995, was arrested Monday in a raid in Serbia that ended a 13-year hunt.

Serge Brammertz, the prosecutor of the United Nations war crimes tribunal in The Hague, hailed the arrest as an important step in bringing to justice one of the architects of Europe’s worst massacre since World War II. He said Mr. Karadzic, 63, the Bosnian Serb president during the war there between 1992 and 1995, would be transferred to The Hague in “due course.”

“This is a very important day for the victims who have waited for this arrest for over a decade,” Mr. Brammertz said. “It is also an important day for international justice because it clearly demonstrates that nobody is beyond the reach of the law and that sooner or later all fugitives will be brought to justice.”

Mr. Karadzic’s exact place of arrest was not announced, but Serbian government officials said he was arrested by the Serbian secret police not far from Belgrade, the capital. Officials from President Boris Tadic’s office said Mr. Karadzic had appeared before an investigative judge at Serbia’s war crimes court, a prerequisite for his extradition to The Hague.