SAO PAULO (AP) — Brazilian authorities say nine men have been killed in a string of attacks following the slaying of a police officer in the northern city of Belem.

The public safety department of the state of Para says assailants arrived by motorcycle in several of the attacks, four of which occurred in the same neighborhood.

Police Chief Luiz Fernandez said Wednesday that officials are investigating whether the cases are related to the slaying of 43-year-old Antonio Figueiredo, an officer of a special tactical team who was off duty.

Fernandez says it remains unclear whether members of the police force were involved in the subsequent attacks. There were no reports of police clashes after the officer was killed.

The government has also called on Para's public safety department's internal affairs unit to investigate.