Two men and two women have been arrested following the discovery of a suspect package at a house in the Abbeyfield area of Killester.
The first arrest was made at the house at 6.30am this morning.
The package was discovered as part of an ongoing investigation into a suspect device which was found at the Shell Building on Leeson Street in Dublin on 15 September.
The four are being questioned at Garda stations at Pearse Street, Donnybrook, Kevin Street and Harcourt Terrace.
A Defence Forces explosive ordnance disposal team found that the package was a hoax.
Another suspect device on the Ballymount Road in Dublin was later examined, and was also found to be a hoax.
A section of Catherine St in Waterford city was closed off following the discovery of a suspect device.
Gardaí were carrying out a search of a vehicle parked on Catherine St when the discovery was made.
The area was evacuated and Waterford district court, which is on Catherine St, was adjourned for the afternoon.
A Defence Forces explosive ordnance disposal team arrived on the scene at 4pm and foundd it to be a viable improvised explosive device.
The device was dismantled and made safe at the scene, which was declared safe at 5pm.