Four members of an outlaw motorcycle gang have been arrested in police raids on 23 Victorian properties, as part of an investigation into a man's death on Australia Day.
About 300 police were involved in the raids about 6am on Tuesday, which targeted seven clubhouses and other properties with links to the Rebels outlaw motorcycle gang.
The properties, some of them fortified, were across Melbourne, Geelong and Traralgon.
Four men, two of them Rebels bikies, have already been charged with the murder of 20-year-old Michael Ali Sleiman, who died after 15 people allegedly stormed a Deer Park house on January 26 and started a fight.
Victoria Police assistant commissioner Stephen Fontana said the operation was to arrest a number of other members of the outlaw motorcycle gang that police believed were involved.
"It wasn't bikie on bikie - this was an act of a group of bikies who targeted another person that wasn't associated with outlaw motorcycle gangs," Mr Fontana told reporters outside one of the properties in Sunshine West.
"We currently have four persons in custody from this particular outlaw motorcycle gang that we believe are involved in this homicide and they are currently being interviewed."
The operation was supported by Customs and Border Patrol and the Australian Federal Police national anti-gangs squad.
Police also found drugs, firearms, and a suspected stolen vehicle during the raids and Mr Fontana said searches at the properties would be continuing through the day.
The four men who have been charged with Mr Sleiman's murder remain in custody and are due to appear in court again in November.