A haul of around 20 million contraband cigarettes was today seized from a ship docked on the east coast, the Revenue Commissioners said.
Revenue Enforcement Division officers boarded the vessel in Dundalk harbour, Co. Louth, after a surveillance operation led by the Navy.
"It could take several days for the exact value of the cigarettes to be established," a Revenue spokeswoman said.
"The cigarettes were concealed in a consignment of timber on the ship which had sailed from Muuga, near Tallinn in Estonia," the spokeswoman said.
"The number of cigarettes has yet to be firmly established but it is provisionally estimated at 20 million. This would represent a revenue loss of £3 million," she added.
A number of men are currently being interviewed by customs officers.
A ship which was yesterday impounded at Drogheda harbour in Co Louth, as part of an investigation into smuggling operations by dissident Republicans, contained no illegal cargo.
The ship was held at the port during a joint operation between customs and Gardaí.
But a Garda spokesman said today the ship was found to be legitimate and the search operation has ended.