A man has been arrested after he arrived at St Patrick's Institution this morning carrying a loaded gun.
The 37-year-old man was driving a waste disposal truck to the juvenile jail, which is in the Mountjoy Prison complex.
When the driver was asked at the security checkpoint if he had anything on him that he should not have, he showed them a loaded Walther semi-automatic pistol and two cartridges with 14 rounds of ammunition.
The handgun was taken from the man by prison officers.
Gardaí from nearby Mountjoy Garda Station were called in and the man was arrested.
Detectives are now trying to establish where he got the gun, how long he had it and why.
While the man may have had a licence for the weapon in his home country, Romania, he did not have it licenced in Ireland.