A substantial shipment of drugs valued at up to €100 million was transferred from a 'mothership' to a smaller vessel off the Kerry coast in the early hours of Monday.
RTÉ News understands that the transfer is believed to have taken place a significant distance offshore.
Investigating gardaí are understood to be making progress on piecing together the jigsaw of what happened off the Kerry coast late on Sunday night and early on Monday morning.
It is understood that the drugs were not destined for the Irish market and that they are no longer in this jurisdiction.
Further developments in the operation, which is being led by the Garda Drugs and Organised Crime Bureau and Revenue's Customs Service, are expected in the coming days.
Five men ranging in age from their late 20s to their mid-40s are currently being questioned by detectives in counties Kerry and Clare.
Four of the men were arrested by gardaí at 5.20am on Monday morning, after they arrived back on a rib at a pier at Meenogahane in north Kerry.
Night vision and satellite navigation equipment, along with a number of encrypted mobile phones were also seized.
A fifth man was arrested after gardaí and Customs officers boarded a cargo ship at anchor in the Shannon Estuary yesterday afternoon.
The ship was searched and no drugs were found.
The ship had left Brazil on 26 December 2024.
Investigators are satisfied that it was en route to Ireland with a legitimate cargo and that the drugs had been hidden on board.
When contacted for comment, a garda spokesperson said "An Garda Síochána does not comment on on-going operations".
