An investigation was under way last night into the source of 125 kilograms of commercial explosive found in a Real IRA hideout in north Galway.
Gardai believe the explosives had been stolen from a quarry and checks are being carried out to determine if any substantial quantities had recently gone missing from a commercial firm.
Officers will now try to establish whether the explosives seized in an operation on Wednesday night and early yesterday morning had been taken recently or had been stored in a dump for several years.
The find was described as being in good condition.
The explosives were discovered in five 25kg bags in an outshed attached to lands outside the village of Monivea. In a nearby farmhouse, gardai recovered one handgun and three shotguns.
A 48-year-old local man was arrested at the scene and taken for questioning to Mill Street Garda Station in Galway city.
In a follow-up operation, gardai searched a house on the outskirts of Tuam and recovered another firearm. A married couple were arrested and they were also being questioned last night in Galway.