It's understood that five men will appear before a special sitting of a Killarney District Court later this evening.
Four of the five were arrested in Kerry in the early hours of Monday, on suspicion of assisting organised crime in the importation of controlled drugs.
They had their period of detention extended at a sitting of Killarney District Court on Tuesday night.
A fifth man was arrested in on Wednesday following the search of a cargo vessel on the Shannon Estuary.
Revenue Customs officers, supported by members of the Garda National Drugs and Organised Crime Bureau, had boarded and searched a cargo vessel that was anchored in the Shannon Estuary.
Gardaí said at the time that the arrest of the 28-year-old man was connected to the arrests of four men in Kerry.
The men were being held in Killarney and Tralee Garda stations, as well as a Garda Station in Clare, and include a Serbian National, with an address in Manchester; a man with an address in Derry; and two men with addresses in Glasgow.
Gardaí say investigations are ongoing.