Gardaí arrested two men and seized explosives in Co Louth in an operation assisted by the army bomb squad on Friday.
Component parts and suspected explosive material were seized in the search, assisted by the Defence Forces Explosive Ordnance Disposal (EOD) team.
Two men, one in his 50s and another in his 20s, have been arrested as part of the investigation.
Both are currently being detained at Garda stations in the northeast of the country under the Offences Against the State Act, 1939.
Garda Commissioner Justin Kelly said: “This is a particularly significant find. This search and arrest operation by our counter-terrorism unit, the Special Detective Unit (SDU), demonstrates the important work carried out by Garda national security personnel every day to protect people on this island.
“It also shows that we must continue to degrade and dismantle the threat from those who are intent on destroying peace by harming others.”
He added: “I have been in contact with the PSNI Chief Constable Jon Boutcher this morning and our close co-operation in relation to countering dissident groups continues. I would also like to thank the Defence Forces for its assistance in today’s search operation.”