Gardai have uncovered a dissident bomb making operation after a swoop on a disused quarry in the Republic.
Senior sources within the force believe the devices being made were designed for use in deadly car bomb attacks on members of the PSNI.
The find was made after a Garda investigation lasting almost two years.
Three suspected dissident republicans were arrested when members of the emergency response unit led the Garda swoop on the quarry.
Last night searches were continuing in an area bordering counties Carlow, Kildare and Wicklow.
Two men in their 40s, with addresses in Drimnagh and Finglas in Dublin and a man in his 50s from Carlow are all being questioned at Garda stations in the Dublin area.
One of the suspects has links to Northern Ireland.
The three are being held under anti-terror legislation and can be detained without charge for up to three days.
Senior officers believe a dissident group with links to the New IRA has been using the quarry to make bombs, particularly devices for use under vehicles.
Some of the group may have had links in the past to the INLA.
Gardai believe they have smashed a “significant manufacturing operation based at the quarry and elsewhere”.
Officers believe those involved were highly experienced in terrorist engineering.
The arrests follow a huge intelligence gathering and surveillance operation that began shortly after detonators were found in the south east of the Republic in the past two years.