BELGRADE, Yugoslavia (AP) _ In the latest in a series of assassinations here, a top official of Slobodan Milosevic's ruling party was shot and killed Saturday by an assailant who walked up to him at a fair, pressed a gun to his head and pulled the trigger.

Bosko Perosevic was touring the agricultural fair in the northern city of Novi Sad when a security guard at the fair compound shot him, reporters who were at the scene said.

Perosevic, the chief of the Socialist Party branch in Novi Sad and the head of regional government for the northern Vojvodina province, was rushed to a Novi Sad hospital. The head of the hospital, Djordje Janic, said Perosevic died there Saturday afternoon.

Witnesses at the scene said the gunman was a longtime exhibition employee. They and reporters identified him as 50-year-old Milivoj Gutovic. Belgrade-based Studio B Television said the attacker had known Perosevic for years and that both were born and raised in the same town.

Police arrested the gunman after a brief chase, the private Beta news agency and witnesses said.

The incident happened at about noon at a cattle display within the agricultural fair, held annually in Serbia's second-largest city, about 45 miles northwest of Belgrade.

Studio B reported that seconds before the attack, Perosevic's mobile telephone rang and he moved away from his delegation of government officials. As he answered the phone, the gunman approached him and fired.

It was unclear whether the shooting was politically motivated. But it was the latest in a series of high-profile assassinations or attempts against government officials, top businessmen and underworld figures here. The general manager of Yugoslav national carrier, JAT, was killed last month, and the country's defense minister was shot dead in February.

Investigations in previous cases have not been conclusive. This is the first time the alleged attacker has been apprehended on spot.

A statement from the Socialist Party condemned the attack, saying the party expects police ``to efficiently solve what is behind this assassination.''