Fugitive war crimes suspect Ratko Mladić was arrested on May 26 2011, Serbian president Boris Tadic was quoted as saying by media in Belgrade.
A man, identified in Serbian media reports as bearing the name Milorad Komadic, was being held in custody by Serbian authorities who suspected him of being Mladic, Belgrade media said. Identity tests, including DNA, were being conducted to confirm he was Mladić, reports said.
A family friend had said that the man was Mladić, the BBC said, quoting news agency Reuters.
Mladić has been in hiding since 1995, after the International Criminal Tribunal for the former Yugoslavia charged him with war crimes and crimes against humanity during the 1992/95 Bosnian war.
Among crimes of which Mladić is accused is the July 1995 Srebrenica massacre.
The handing over of war crimes suspects, especially Mladić, has been repeatedly emphasised to Serbia as a precondition for its European Union ambitions.
Last week, the United Nations chief prosecutor for the war crimes tribunal, Serge Brammertz, said Serbia has not done enough to capture Mladić and another top fugitive suspect, Croatian Serb Goran Hadzic, the Voice of America said.
Brammertz said Belgrade must prove it wants to fully co-operate with The Hague-based court with concrete action and visible results.
Brammertz will present his report to the UN Security Council June 6.
EU officials have made delivering Mladic a key condition for granting Serbia EU-candidate status.