A huge car bomb was found in Dublin hours before the climax of the Irish leg of the Giro d'Italia cycle race.
The 230kg bomb, made from fertiliser mix, was discovered on Saturday night in the car park of a hotel in Lucan, west Dublin, police said. The car had Belfast-registered number plates.
Dissident Northern Ireland republicans are being blamed for the device.
A Belfast man, 55, was arrested on Sunday in the Irish capital in connection with the bomb and is being questioned by detectives.
The Giro d'Italia opened in Belfast on Friday and Sunday's stage three took riders from Armagh to Dublin.
Tens of thousands of people lined the route in Dublin to cheer on the cyclists, with millions more watching worldwide.
The suspect is believed to have had links with the hardline Continuity IRA, although he has more recently been linked with the New IRA terror alliance.
The movement of a huge explosive device from Northern Ireland to the Republic would be highly unusual; so-called "terrorist traffic" more often goes the other way across the border.
The device, which was hidden inside a milk churn, contained a sophisticated timer similar to those used by the Provisional IRA during 30-year nationalist conflict in Northern Ireland that ended in 1998.
Police found bomb-making material, including mercury tilt switches, in a follow-up search at a property in central Dublin.
Irish army bomb disposal experts made the device safe at the scene but hundreds of guests attending a wedding at the Finnstown Country House had to be evacuated on Saturday night.
The bomb scare came amid heightened tensions over the arrest in Northern Ireland earlier this month of Gerry Adams, the leader of the Republican Sinn Fein party, over a notorious IRA murder in 1972.
Additional reporting by Agence France-Presse