A teenager from Brighton had to have stitches in his lip after being attacked in the town centre in the early hours of Saturday (31 March).
The 19-year-old victim was walking along East Street with two friends when he was attacked at the junction with Bartholomews at about 2.45am.
Sussex Police said: “They were approached by a group of three Asian men, one of whom attacked the victim, causing a serious injury to his lip which needed stitches.”
Detective Constable Aran Boyt, the investigating officer, said: “At this time the circumstances as to what happened are a little unclear and we are hoping that someone will come forward who either witnessed what happened or has information about the incident.
“The victim was left with a very nasty injury to his face and we are anxious to establish how and why this happened.”
Anyone with information is asked to contact Sussex Police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.
