The 1.5 tonnes of cannabis resin seized when the authorities boarded a vessel off the west Cork coast early yesterday originated in Morocco, and is believed to have been intended for export to continental Europe after being landed in Ireland.
A combined naval, customs and Garda operation resulted in the confiscation of the cannabis, estimated to have a street value of £15 million. One senior Garda source said the seizure was the result of international liaison and local knowledge.
Three British nationals are being held for questioning at Bandon Garda station.
Once their vessel, the British-registered Posidonia, was escorted to Schull pier early yesterday morning, they were held for an initial six hours under Section 2 of the Drugs Trafficking Act.
The detention was later extended under the order of a chief superintendent, and the period may again be extended for a further 24 hours from 2 a.m. this morning.
It is understood that police forces in Britain and elsewhere are being consulted in an effort to determine precisely how the shipment was organised and who was behind it.
The Posidonia was apparently in poor condition and making slow headway on its journey from Morocco to the Cork coast, where it was intercepted by the Irish naval vessel, Le Ciara, on Tuesday afternoon.
There was a news blackout on the interception while customs officials and gardai prepared their plan.
The Ciara, commanded by Lieut Cdr Martin McGrath, picked up four members of the combined operation force off Baltimore, and two armed boarding parties were launched.
Cannabis resin was found strewn about the wheelhouse of the boat, which was then escorted to Schull early yesterday.
Other gardai were standing by at the pier to arrest the three British nationals, two of whom were said to be in their 50s, while the third was aged 32. He gave a London address, which is now being checked by gardai.
A forensics team is examining the boat, most of which is expected to be dismantled to determine whether even more drugs may have been concealed in secret compartments.
The £15 million haul came only hours after almost £1 million worth of ecstasy tablets were found at a warehouse near Glanmire, on the outskirts of Cork city, on Tuesday night.
Following a prolonged surveillance operation, gardai found at least 75,000 ecstasy tablets, which they think were destined for distribution in Cork city and the Munster counties.
Four men in their 30s were arrested under Section 2 of the Drugs Trafficking Act. They were detained at the Mayfield and Gurranabraher Garda stations in Cork. It is understood that one of the men has an address in Nottingham, while the others are from Cork city and county.