The assassination of Serbia's prime minister was orchestrated by a group that wanted to replace the pro-Western government with allies of Slobodan Milosevic, investigators said today.

The group behind the killing of Zoran Djindjic on March 12 -- called the Hague Brotherhood because its members oppose the U.N. war crimes tribunal in The Hague -- hoped the assassination would create chaos and planned to follow with a coup attempt against Serbia's government, the officials said on condition of anonymity.

But Djindjic's Democratic Party quickly named a successor and police cracked down hard, arresting 7,000 people, effectively spoiling the plan. The assassins may also have been caught off-guard by the huge public outpouring of grief over Djindjic's death. Nearly 1 million people attended his funeral.

Police said they believed a feared paramilitary group known as the Unit for Special Operations, formed during Milosevic's rule, played a large role in the Hague Brotherhood. Its deputy commander, Zvezdan Jovanovic, was arrested soon after Djindjic's slaying on suspicion of being the assassin. The officials said Jovanovic told investigators that he killed Djindjic because he was told his unit would be handed over to the war crimes tribunal.