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.