A murder investigation is under way following the death of a 20-year-old man in Dublin.

The man was found with serious head injuries on the Old Blessington Road at around 3am on Wednesday 1 November and taken to Tallaght Hospital.

He was later transferred to Beaumont Hospital where he died today.

Gardaí upgraded the investigation to murder following a post-mortem examination.

A 20-year-old man was arrested in Tallaght this afternoon in relation to the investigation and is being held at Tallaght Garda Station.