Zdravko Tolimir, a former senior aide to the Bosnian Serbs' wartime military commander, Gen. Ratko Mladic, during the slaughter of more than 8,000 Bosnian Muslims in Srebrenica, in 1995, was detained in Bosnia-Herzegovina Thursday.
After a medical check, he was flown from the Bosnian capital Sarajevo on a NATO helicopter.
Official sources said the former general is ill, possibly with cancer.
Tolimir was indicted in 2005 by the UN tribunal with genocide, conspiracy to commit genocide, extermination, murder, persecution, forcible transfer and deportation, as well as murder in connection with the Srebrenica massacre.
The International Criminal Tribunal for the Former Yugoslavia has yet to find Serbian General Ratko Mladic and former Bosnian Serb leader Radovan Karadzic to try them for war crimes, genocide and crimes against humanity.