Two people are being questioned after gardaí intercepted a sophisticated explosive device hidden inside a car travelling towards the border with Northern Ireland.
The bomb was discovered during an intelligence-led operation near Carrickmacross, Co Monaghan, after officers stopped the vehicle on the N2 on Wednesday.
Bomb disposal experts from the Defence Forces were called to the scene and safely defused the device before it was taken away for forensic examination.
According to gardaí, the bomb had already been fully assembled and was ready to be used.
Garda Commissioner Justin Kelly described the discovery as an "extremely significant" seizure.
"This was an explosive device and it would have or could have potentially caused significant damage," he said.
Investigators believe the device was intended for use in an attack in Northern Ireland. It is understood to have contained military-grade explosives, a detonator and its own power source.
Commissioner Kelly said the stop was part of an ongoing investigation into dissident republican activity and stressed it was not a random checkpoint.
He also expressed concern that extremist groups continue to recruit younger people.
"There's a small minority of these individuals... I would describe them as radicalised republicans," he said, adding that gardaí are continuing to work closely with the PSNI and UK intelligence agencies to tackle the threat.
A woman in her 20s, who was driving the vehicle, was arrested at the scene, while a man in his 40s was later arrested in the Dublin area. Both are being detained under the Offences Against the State Act.
Justice Minister Jim O'Callaghan said the incident demonstrates that the threat from dissident republican groups has not disappeared.
He described the discovery as "very worrying" but commended gardaí for intercepting and safely defusing the device before it could endanger the public.
The seizure comes as security services on both sides of the border continue to monitor the activities of a small number of dissident republican organisations that remain opposed to the Good Friday Agreement.
