Detectives are appealing for witnesses after the report of a serious assault in the early hours of this morning.
The incident happened in the Waterside area of Londonderry.
Detective Sergeant Ray Phelan said: “Shortly before 1.40am 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.
"NIAS paramedics responded minutes later and discovered three men, two in their 30s and one in his 40s with injuries sustained as a result of what appears to have been a violent attack.
"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.
"We are working to establish how the men sustained their injuries, who was responsible, what the circumstances were leading up to the incident and we are making a number of appeals.
"Were you in the Bonds Street or Lower Glendermott Road area between 1am and 1.40am this morning? Did you see any suspicious activity? Did you see a number of men walking along Bonds Street armed with hammers?
"We are keen to hear from anyone who was socialising in licensed premises on the Dungiven Road last night, and who witnessed any type of altercation.
"Anyone with information is asked to contact detectives at Strand Road on the non emergency number 101, quoting reference number 154 of 13/05/18.
"Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”