Police in Croatia have arrested a number of men and seized a shipment of missiles, machineguns and explosives believed to have been on its way to dissident republicans in Ireland.
The weapons were seized earlier this week in the Adriatic holiday city of Split.
Exact details of the haul were not available last night but it is believed the shipment contained plastic explosives, machine-guns, ammunition and detonating cord.
It is understood a number of senior Garda Special Branch officers travelled to Split after the discovery.
The number of men arrested there is not known; the only available information was that they were being "processed" through the criminal justice system in Croatia.
No Irish people were reported arrested in Croatia, but after the find, gardai in Co Louth arrested a man from the Border area on Wednesday who is reputed to head the group known as the Continuity IRA.
He was arrested under Section 30 of the Offences Against the State Act, which allows his detention for three days.
He is being held in a Border Garda station.
Members of the Garda's specialist arms unit, the Emergency Response Unit (ERU), travelled to the Border area this week and further arrests are expected. There were no reports of further arms finds.
The weapons discovery is understood to have followed a trans-national police operation in which arms buyers from both the Continuity IRA and the other dissident republican group, the "Real IRA" were tracked through Holland across Europe to the Balkans and the Middle East.
The operation had been going on for months.
It is understood the arms seizure was made by local police, independent of help from outside police.
It is known that gardai had information that men from south Armagh, north Louth, and Fermanagh were involved in arms buying for the dissident organisations.
The arms-buying operation is said to be under the direct control of a Dundalk, Co Louth man, a former leading Provisional IRA member who left the organisation after a dispute over support for the ceasefire in October 1997. With the aid of a woman, he set up the "Real IRA", which was subsequently responsible for the Omagh bombing atrocity.
The leadership of the "Real IRA" is understood to have struck a deal with the Continuity IRA leadership over arms buying.
It appears the Continuity leader, originally from Co Monaghan but living in Newry, established contact with the Croatian arms dealers over a year ago.
The Continuity IRA leader has been arrested on a number of occasions, once after a large amount of home-made explosive was found in Inniskeen, Co Monaghan in 1992. But he has never faced serious charges here or in Northern Ireland.
It is believed this man subsequently agreed to lead the "Real IRA" to the source, so long as it financed the shipment.
"Real IRA" members from south Armagh are understood to have travelled as part of the arms-buying team.
Finance for the arms buying reportedly came from smuggling and other criminal activity in the Border area. A senior "Real IRA" figure in the Border area north of Dundalk is said to be one of the largest suppliers of smuggled cigarettes in the region.
The two dissident organisations have been working in unison for the past year, sharing equipment and ideas.
The arms discovered in Split are said to be identical to weapons found by gardai on a farm at Stamullen, Co Meath, last October. That cache included RPG18 rockets, plastic explosives and electric detonators.
Gardai are unsure how many weapons were smuggled into this State in the past year.
Sources say the weapons coming from former Yugoslavia have been of very high quality. The RPG18 rocket is an anti-tank weapon more powerful than any used by the Provisional IRA.
The dissidents also have an unknown supply of a very powerful explosive similar to the Semtex explosive held by the Provisionals. They also have electrical detonators.