Authorities believe that five million contraband cigarettes worth an estimated €1.5 million which were seized in Cavan on Wednesday night were brought into the country by an Irish-based crime gang with international links.
The seizure, one of the largest of its kind this year, followed weeks of surveillance which culminated in a raid on a farmhouse in Cootehill, Co Cavan, at 10pm on Wednesday.
The raid was led by Customs officers who were assisted by armed gardaí from Cootehill Garda station.
The officers had monitored the consignment of cigarettes, which had been imported from South America, after it arrived at Dublin Port on Sunday.
The cigarettes had been concealed in bales of plywood that had been shipped in a 40ft container which originated in Paraguay.
The MP brand cigarettes were kept under surveillance as they were transported to Cootehill on Wednesday. They were placed in a warehouse before being seized by Customs officers.
It is believed the haul was brought into the country by a well-organised Irish criminal organisation which has international connections. However, it remained unclear last night if there were any links with dissident republican groups.
A Revenue spokesman said the raid followed a "lengthy operation" that involved both the Dutch and Belgian customs services and OLAF, the European Commission Anti-Fraud Office.
"Several persons were interviewed at the premises but no arrests were made," the spokesman said. "Investigations are ongoing both nationally and internationally . . . A file may be sent to the Director of Public Prosecutions."
The cigarettes are valued at €1.5 million, with potential loss of revenue amounting to €1.2 million, according to the Revenue spokesman.
Wednesday night's haul is the latest in a series of such seizures by Revenue officials in recent months.
Last June Customs officers at Cork airport seized more than 56,000 cigarettes with an estimated street value of €17,600. The cigarettes originated in Lanzarote, the Canary Islands, and were concealed in suitcases carried by two English women.
Last May Customs officers seized five million Palace brand cigarettes with an estimated street value of €1.7 million. The contraband cigarettes arrived in a container by ship from Oporto, Portugal, and were packed on pallets in a container of textiles and footwear.