European Union peacekeepers in Bosnia on Tuesday searched houses belonging to the family of Bosnian Serb wartime general Ratko Mladic, the last remaining high-profile war crimes suspect from the 1992-95 war.

"The aim of the operation was to look for information which could assist the ongoing search for Ratko Mladic, as part of a wide regional strategy ... against potential support network in Serbia," said EUFOR spokesman Patrick O'Callaghan.

The arrest of Mladic, thought to be in hiding in Serbia, is a key condition for Serbia's progress towards the EU membership.

Last July his erstwhile boss Radovan Karadzic was captured. He is now on trial in The Hague.

The 10-hour-long operations at two sites in East Sarajevo, the section of the Bosnian capital located in the autonomous Serb Republic, were launched early on Tuesday on the orders of the U.N. war crimes tribunal and completed in the afternoon. Evidence was taken away to be analysed by EUFOR and NATO.

"The ICTY (International Criminal Tribunal for the Former Yugoslavia) was trying to gain as much new information it could to cut off the financial network and try to find more on Mladic's logistics and finances," O'Callaghan told Reuters.

The Portuguese troops serving with EU peacekeepers and supported by NATO and the Serb Republic police raided the houses of Mladic's sister Milica Avram and sister-in-law Radinka Mladic. Both families were cooperative, O'Callaghan said.

The U.N. war crimes tribunal in The Hague indicted both Karadzic and Mladic of genocide over the 1995 Srebrenica massacre of 8,000 Bosnian Muslims and the 43-month siege of Sarajevo in which thousands were killed.