Army bomb experts have described as "viable" two devices discovered during a series of raids during which six men were arrested for suspected terror offences.
Garda sources say there is no direct link at this stage or any evidence of a credible plot related to a visit to the west of Ireland next week by the Prince of Wales and the Duchess of Cornwall.
During the trip, Charles will stop at Mullaghmore, Co Sligo, where his great uncle Lord Mountbatten was assassinated by the IRA in 1979.
Some 20 searches were carried out yesterday as part of a Garda investigation into dissident republican activity in counties Dublin, Louth and Wexford.
Four men arrested on suspicion of a number of offences, including directing terrorism, membership of an unlawful organisation and possession of explosives, are being held at a number of Garda stations in Dublin.
One of the detained suspects is in his 60s and the other three are in their 20s.
It is understood that a "leading figure" in the republican movement is among those being detained.
They are being questioned under the Offences Against the State Act and can be held for 72 hours.
Separately, a firearm and component parts for explosives were discovered at Glenfarne in Co Leitrim yesterday, around 25 miles from Sligo, when a car was stopped by a traffic enforcement officer.
Two men in their 20s arrested at the scene are also being held under the Offences Against the State Act, at Manorhamilton Garda station.
Army bomb experts said two improvised explosive devices made safe in Leitrim were viable.
Bomb-making equipment made safe at Courtown, Co Wexford, and Dromiskin, Co Louth, is being examined by the Garda.