The former Bosnian Serb leader and war crimes suspect, Radovan Karadzic, is hiding in Montenegro, international security agencies have told the BBC.
Peacekeeping troops in neighbouring Bosnia cannot take action as their jurisdiction does not cover Montenegro, which is part of Serbia and Montenegro.
Mr Karadzic has been on the run for the past eight years.
He has been indicted for genocide by the UN war crimes tribunal in the Hague for his part in the Bosnian war.
Speaking on condition of anonymity, sources close to the investigation have told BBC Radio Four’s File on Four programme that Mr Karadzic is believed to be in a remote part of north-west Montenegro.
They say they have reliable intelligence that he is living not far from the town of Niksic, where he grew up.
It is the first time such definitive information on his location has emerged.
The area is mountainous and sparsely populated and has a tradition of hardline Serb nationalism.
Separate security sources have told the BBC that Mr Karadzic is no longer living in Bosnia.
Mr Karadzic led the Bosnian Serbs during the three-and-a-half year Bosnian war in the early 1990s.
The UN War Crimes Tribunal has indicted him for genocide for, among other alleged crimes, the massacre of nearly 8,000 Muslims near the town of Srebrenica in July 1995.
Mr Karadzic’s former military commander, Ratko Mladic, is also on the run.
There has been increasing pressure on the local authorities in Bosnia and Serbia and Montenegro to track down the two fugitives in time for the 10th anniversary of the Srebrenica massacre next week.