“Detectives are working to establish the full circumstances surrounding Thursday’s incident, including the actions and movements of those involved before, during and after the disorder.
“At this stage of our enquiries, we believe the violent disorder involved members of two rival Outlaw Motorcycle Clubs, the Vikings and the Hells Angels.”
In an update on Tuesday, the senior investigating officer said police were “working around the clock” to identify everyone involved and “bring those responsible before the courts”.
The family of the victim are being supported by specially trained officers.
“Our thoughts remain with the family of the victim,” she said.
On Monday, Gwent Police appealed for Anthony Paul Jones, 40, from Blaenavon, Torfaen, to come forward as part of the investigation.
Officers are also looking for a blue Ford Transit van with the registration MA23 FLC that was reportedly involved in the disorder.
The van is believed to be missing its front lower nearside panel.
The men arrested are aged between 31 and 73, and three have been released on bail, the force said on Monday.