PSNI detectives in Derry are appealing for witnesses following reports of a serious assault in the Waterside area in the early hours of Sunday morning.
Police received a report from a member of the public that a number of men were seen walking along Bonds Street armed with what was described as a sledgehammer and hammers shortly before 1:40am.
Paramedics responded and discovered three men, two aged in their 30s and one in his 40s, with injuries from what appears to have been a violent attack.
Detective Sergeant Ray Phelan said: "We believe the three men were the victims of an unprovoked and cowardly attack by four assailants armed with weapons.
"Police are exploring a potential link to loyalist paramilitaries as part of our enquires."
They are keen to hear from anyone who was socialising in pubs on the Dungiven Road, and who witnessed any altercation.