Serbia declared a state of emergency yesterday after the Prime Minister, Mr Zoran Djindjic, was shot dead. Mr Djindjic (50) was hit twice in the chest in front of the main government headquarters in the capital, Belgrade, at 12.45 p.m.
The Serbian government last night named a former head of a police unit as one of the leaders of a criminal gang it accused of being behind the assassination of the prime minister.
The government said Milorad Lukovic, also known as Legija, was one of around 20 named leaders of a group it called the Zemun clan, named after a Belgrade municipality.
"The assassination of Serbian Prime Minister Zoran Djindjic represents an attempt by this group to stop the fight against organised crime that just started and for them to avoid their own arrest," the government said in a statement.
Three men were arrested soon afterwards as a massive security blanket was thrown across the city.
Mr Djindjic underwent emergency surgery in hospital but died soon afterwards.
Witnesses said a volley of shots rang out from one or possibly two snipers, wounding one other man.
The government declared a state of emergency, closing all airports and ordering security forces to guard strategic locations.
Roadblocks were thrown up on all roads leading into the capital.
Police checkpoints, some apparently thrown up by the officers themselves without specific orders, were stopping dozens of vehicles across the city.
Army units across the country went on alert.
At an emergency session of the Serbian government, Deputy Prime Minister Mr Nebojasa Covic was named as acting prime minister.
The assassination comes one month after an earlier apparent murder attempt when a truck swerved into the lane taken by Mr Djindjic's motorcade on the way to Belgrade airport.
Mr Djindjic was seen as the prime mover of a reform effort designed to rehabilitate a country that had been, for a decade, an international pariah under the rule of Mr Slobodan Milosevic.
His death leaves a huge question mark over whether Serbia will continue its reform process or fall back into hardline nationalism.
For the West, his death comes at a difficult time, with America hoping to scale down its involvement in the Balkans.
With Mr Djindjic at the helm, Serbia had been making progress on key diplomatic fronts.
He had begun to speak of normalisation in the southern province of Kosovo, where tension is still high between Serbs and Albanians.
And the country had made progress with war crimes, with a slew of top war crimes suspects, including former Serbian president Mr Milan Milutinovic, sent to The Hague under Mr Djindjic's orders in recent weeks.
Both policies are now in peril, as is Mr Djindjic's drive to reform an economy still dominated by state industries left over from the communist era.