The resignation was not a surprise as Rasim Ljajic had vowed to step down if he failed to bring Serbia's most high profile war crimes suspect to justice this year.

"This is to inform you that for reasons well known to everybody ... I resign from my post" (as head of the unit), Ljajic said in the letter submitted to Serbian Prime Minister Mirko Cvetkovic.

But this does not mean Ljajic is giving up completely. He will remain head of the National Council for Cooperation with the Hague Tribunal, a separate body. He will also stay on as Serbia's labor minister.

High-profile criminal

Mladic is wanted for genocide and crimes against humanity for his role in the 1995 massacre of more than 7,000 Muslims in Srebrenica. His capture is a key condition in Serbia's bid to join the European Union.

Mladic was indicted in 1996 by the tribunal in The Hague. He and Croatian Serb wartime leader Goran Hadziic are the only remaining tribunal indictees still at large. Both are believed to be hiding in Serbia.

th/dpa/AFP/AP

Editor: Susan Houlton