Serge Brammertz, who has been leading a U.N. probe into the killing of Lebanese Prime Minister Rafik al-Hariri, has been named to succeed Carla del Ponte has prosecutor for war crimes in former Yugoslavia.

In a letter to the Security Council made public on Tuesday, U.N. Secretary General Ban Ki-moon said he was nominating the Belgian prosecutor to succeed del Ponte in a move widely predicted since she said she would step down at the end of this year.

Del Ponte led the war crimes tribunal for Yugoslavia for eight years and helped bring a number of suspects to court, including former Serbian President Slobodan Milosevic, who died last year before his trial could be completed.

She has long been pressing Serbia to arrest and hand over Bosnian Serb leader Radovan Karadzic and his military commander, Ratko Mladic, whose fate is key to Serbia's progress towards European Union membership.

Mladic and Karadzic are indicted for the July 1995 Srebrenica massacre of 8,000 Muslims. Two other ethnic Serbs, Goran Hadzic and Stojan Zupljanin, are also wanted for crimes committed in Croatia and Bosnia respectively.