The PSNI are investigating whether or not a loyalist gang were responsible for a hammer attack that left three men in hospital this morning.
Detectives are appealing for witnesses following the report of the serious assault in the Waterside.
Police said the attack was unprovoked.
Detective Sergeant Ray Phelan said: “Shortly before 1.40 a.m. 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.
"All three men were taken to hospital by the NIAS where they were treated for their injuries, which are not believed to be life threatening at this time.
"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.”
Sinn Féin Councillor Christopher Jackson said: “This was a violent attack and there is shock across the Waterside community on hearing this news emerging.
"I am also very concerned that the PSNI are exploring a potential link to loyalist paramilitaries in this attack.
"I have been warning for some time now about the actions of these groups in the Waterside.
"I have raised concerns about ongoing criminality in the Waterside and the involvement of loyalist paramilitaries in attacks on property, homes and people.
“There needs to be a sustained policing effort to tackle the scourge of paramilitary intimidation and violence and its effect on public confidence.
“It is long past time that all paramilitary organisations left the stage. They are not wanted. They are not supported. There is no rationale for their existence."