The US and the EU have urged Serbia to follow up the arrest of former Bosnian Serb leader Radovan Karadzic by apprehending his wartime military commander as quickly as possible.
Ratko Mladic and Mr Karadzic have been indicted for genocide at Srebrenica, where some 8,000 unarmed Bosnian Muslim men were rounded up, murdered and bulldozed into mass graves in July 1995.
Welcoming the capture of Mr Karadzic, the US Ambassador to the UN, Zalmay Khalilzad, said the US hoped the arrest of Mr Mladic would soon follow.
France, which holds the rotating EU presidency, said the union expected further results.
Lawyers for Mr Karadzic said they would appeal their client's extradition to the International Tribunal at the Hague, where he faces charges of war crimes.
After more than a decade on the run, Mr Karadzic, 63, was arrested on Monday night in Belgrade.
