Two senior gardai have arrived in Croatia to liase with police about the discovery of what is now believed to have been a major arms smuggling operation by dissident republicans.
Meanwhile, Garda sources report that the dissidents have been engaged in a recruitment drive and had been hoping to bolster their organisation with a major shipment of arms from former Yugoslavia.
The shipment seized by Croatian police in the Adriatic town of Split includes RPG18 rocket launchers, plastic explosive, detonators and automatic weapons.
A senior dissident republican figure who was arrested in the Dundalk area on Thursday is still being questioned in Monaghan Garda station. The man is originally from east Monaghan but has been living in Newry, Co Down, in recent years.
Reacting to the find, the North's First Minister, Mr David Trimble, said it was vital for the two governments to work together to fight dissident republican groups.
Speaking after a meeting with the Taoiseach, Mr Ahern, Mr Trimble said the fact that many attempted operations by dissidents had been frustrated proved that when the two jurisdictions co-operated they were effective in preventing paramilitary attacks.
Gardai believe the arms smuggling operation was originated by the Continuity IRA and that it was joined by the "Real IRA", which has provided the finance for the arms buying.
In a similar arms smuggling operation last year, the dissidents managed to acquire several rockets and an amount of high explosive thought to be measurable in stones rather than tons. The latest shipment intercepted in Split is said to be much larger.
It is believed the dissidents have been working hard at recruiting young members and establishing "active service" units inside Northern Ireland to attack security force and commercial property targets.
According to one report the dissidents have been attracting support from former Provisional IRA elements in the Republic. A group of Provisionals in Co Clare is reported to have joined the dissidents in the past month. Garda sources say the dissident groups are still small but are growing.