SEMTEX explosives seized by gardai from a dissident republican depot were part of a haul purchased by the Provisional IRA 30 years ago in Libya, it has been revealed.
The cache contained enough explosives to be used in more than 180 bombs.
Gardai are satisfied that the high-grade military explosive had been stored in a Provisional IRA arms dump that was meant to have been emptied and decommissioned as part of the Northern Ireland peace process.
At the end of the decommissioning, IRA negotiators gave an assurance that all explosives and arms under their control had been "put beyond use".
But anti-terrorist police officers on both sides of the Border have always feared that some of the IRA dumps, under the control of rogue quartermasters, had been untouched.
A detailed forensic examination of the 15kg seized during searches on property at the Old Airport Road in Cloghran, north Co Dublin, last week, has confirmed that they were not recently purchased and had been concealed for more than a decade.
It is not yet known when the explosives came into the possession of the dissident group that stored them in Cloghran.
The haul, which included an Uzi sub-machine gun, 10 revolvers and pistols ranging from Glocks to Walthers, Smith & Wessons and imitation guns and three shotguns, comprised the biggest seizure of arms and explosives by the gardai since the turn of the century.
It was seized following an operation by the Garda special branch and the crime and security section.
Also recovered were electric igniters, detonator cord, pipebombs, a large amount of regular fireworks, a Taser, two silencers, about 1,300 rounds of assorted ammunition (but primarily for 9mm weapons), and a range of electronic equipment, including jammers and scanners to monitor telephone and radio traffic.
Confirmation of the origin of the Semtex is an embarrassment for Sinn Fein although it is accepted that some quartermasters had broken away from the Provisional IRA because of the ceasefire and that they were known to have taken some explosives and weapons with them.
Underlining the significance of the Semtex seizure, gardai said that 80 grammes of the substance had been used in a bomb that killed a PSNI officer in the North. The Semtex is usually used as a booster in bombs and the Cloghran haul was sufficient for about 180 bombs.