Gardai have intercepted a haul of rocket launchers as they were being ferried to Northern Ireland.
As a result of a major surveillance operation, armed detectives last night stopped two cars between Clonmel and Cahir, Co Tipperary, and seized the arms.
Three suspected members of the Real IRA, who are well-known to anti-terrorist detectives in Co Limerick, were arrested during the operation.
Two of the suspects are brothers and all are originally from Limerick city. The third suspect is believed to be the "right-hand man" of one of the brothers, who is in charge of a Real IRA cell that has been highly active in the south-west of the country in the past year.
Members of the cell are regarded as renegades who have switched allegiance between different dissident factions in recent months but are currently aligned to the Real IRA.
The cars were stopped outside Clonmel as they were travelling towards Cahir.
Gardai believe they were likely to have been heading towards Limerick but think the haul was ultimately destined for south Armagh, where the cell hoped to sell the explosives to another terrorist group.
It is understood that four rocket launchers were found when the cars were searched, although gardai said the find had yet to be fully examined by forensic and ballistic experts.
The suspected leader of the gang has been linked in the past to an extortion racket in Limerick, and the cell is also thought to have been behind the production of pipe bombs in the county.
Detectives think the men are linked to a cache of pipe bombs found last December in the village of Murroe, about seven kilometres outside Limerick.
Two of the suspects were taken for questioning last night to Clonmel and the third was being quizzed in Cahir.
They were being questioned under section 30 of the Offences Against the State Act, which allows gardai to detain them without charge for up to three days.
The interception followed weeks of monitoring the activities of the group, and last night's operation involved members of the Emergency Response Unit, the Special Branch and the Republic's National Surveillance Unit.
Gardai in the Limerick-Tipperary area have been clamping down on the activities of the Real IRA in recent months.
A nationwide push was ordered in the wake of the paramilitary display and firing of a volley of shots at the funeral of Real IRA faction leader Alan Ryan on the northside of Dublin last September.