A 29-year-old man was assaulted by six men claiming to be from the Provisional IRA in a so-called paramilitary-style punishment beating in Derry early on Christmas Day.
The man was taken from a bar on Waterloo Street and questioned and beaten before being dumped in the Creggan area.
Meanwhile, detectives are investigating a bomb attack on the Boundary Bar, north Belfast, on Christmas Eve. A device containing nuts and bolts exploded outside the bar shortly before midnight. No one was injured.