The Serbian Government last night claimed a Belgrade-based criminal gang was behind the assassination of pro-reformist Prime Minister Mr Zoran Djindjic.
The authorities say they want to question 20 people in connection with yesterday's killing, including a former commander of a special police unit, Mr Milorad Lukovic - said to be one of the group's leaders.
US President George W. Bush expressed sorrow at the killing, and others urged Belgrade not to be deflected from the path of peace and democracy.
"History will remember Prime Minister Djindjic for his strong leadership during Serbia's successful struggle to end the dictatorship of Slobodan Milosevic," Mr Bush said in a statement.
"Following the peaceful transition to a new, democratic government, Djindjic acted with strength and courage to transfer Milosevic to The Hague, where today he stands on trial for war crimes," he said.
Djindjic (50) played a key role in the downfall of the former Yugoslav president Milosevic, now on trial in The Hague for war crimes committed during the 1990s Balkans conflict.
UN Secretary General Kofi Annan said the killing was a deplorable act of political violence.
AFP