The police intervened immediately because they suspected that the device was a planted explosive.
"We found a package, tied with wires, which contained a brick-coloured powder inside, very wet with no detonator. We do not believe it could have exploded ... we don't believe it could have caused injury," police spokesman Rodoljub Milovic told B92
television.
Party leader Cedomir Jovanovic, 35, was a close associate of Serbian reformist Prime Minister Zoran Djindjic, who was assassinated in March 2003.
Jovanovic is the only politician who has urged Serb voters to ignore promises from mainstream parties that breakaway Kosovo
province, whose 90 percent Albanian majority demands independence from Serbia, can be forced to remain under Serbian
sovereignty with diplomatic backing from Russia.