Ratko Mladic, the Bosnian Serb general wanted for alleged war crimes committed during the 1992-95 Bosnian conflict, has been arrested, Serbia has announced.
"On behalf of the Republic of Serbia we announce that Ratko Mladic has been arrested," Boris Tadic, the country's president, said.
"Today we closed one chapter of our difficult history that will bring us one step closer to full reconciliation in the region.
"All criminals must face justice," he said.
Tadic said the 69-year-old would be extradited to the UN war crimes tribunal in the Hague, but did not give a time frame.
Local media had first reported that a man who identified himself as Milorad Komadic had been arrested and was believed to be Mladic.
Genocide charges
A spokesman for Catherine Ashton, the EU foreign police chief, said she "strongly welcomed" the arrest - "an important step forward for Serbia and for international justice".
Ashton expects "Mladic to be transferred to the International Criminal Tribunal for the former Yugoslavia (ICTY) without delay", Michael Mann wrote on his Twitter account.
Anders Fogh Rasmussen, the NATO secretary-general, said the arrest "finally offers a chance for justice to be done".
Mladic is wanted by the United Nations war crimes tribunal for the former Yugoslavia on charges of genocide during the 1992-95 Bosnian conflict.
He was indicted in 1995 over the Srebrenica massacre of 8,000 Muslim men and boys, and the 43-month siege of Sarajevo, the Bosnian capital, in which around 10,000 people died.
The UN indictment against Mladic says he was the operational mastermind behind the massacre, and also cites the establishment of camps and detention centres for Bosnian Muslims as part of a campaign of ethnic cleansing.
His arrest has been seen as a precondition of Serbia joining the European Union.
Aljosa Milenkovic, a Belgrade journalist, told Al Jazeera that "politicians from the EU have repeated time and again that Mladic is the condition for Serbia's entry" to the bloc.