A murder investigation is underway after a 20 year-old man died in Dublin.

The victim was found on the Old Blessington Road in Tallaght at around 3am on November the 1st.

He was taken to Tallaght Hospital and then to Beaumont with a serious head injury, but lost his fight for life earlier today.

A post mortem was carried out and following this, the investigation has now been upgraded to murder.

It's believed he had been assaulted.

A 20 year old man was arrested in Tallaght earlier today as part of the investigation.

He's being held at Tallaght Garda Station where he can be questioned for up to 24 hours.