The haul was seized from a cargo vessel off the southeast coast of Ireland.

It comes after an elite Irish army unit stormed the Panamanian ship from helicopters on Tuesday.

Speaking at a media briefing in Dublin on Wednesday, a spokesman for the Irish police service An Garda Siochana said: "This is the largest drug seizure in the history of the State."

Three arrests have been made so far, with an investigation ongoing.

Assistant police commissioner Justin Kelly described the action as "hugely significant".

Mr Kelly, from the Irish police's organised and serious crime unit, said: "It shows our unrelenting determination to disrupt and dismantle networks, which are determined to bring drugs into our country.

"These groups are transnational groups. They are working all across the world and, because of that, we need to work with our international partners."

He added the working assumption was not all the drugs on the vessel, which he believes originated from a South American cartel, were destined for the Irish market.

But police think smugglers intended to land the shipment in the country.

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Commander Tony Geraghty, fleet operations officer of the Irish Naval Service, said: "There was an extremely complex joint operation involving the Naval Service, the Air Corps, the Army Ranger Wing and Defence Force headquarters.

"And then it was [made] even more complex by environmentals that we had no control over. The weather was extremely poor.

"And also we were trying to predict the actions of the number of crime gangs and how that would impact on us.

"It was very successful from a Defence Force point of view - it showed the ability we have to operate in the joint environment."

Mr Geraghty added Irish forces fired a warning shot at the vessel from a patrol ship. This came after the vessel failed to comply with their orders.

"The resistance when the [warning] shots were fired was in relation to the manoeuvring of the merchant ship," he said.

"It is compelled under international law to follow the instructions of a commanding officer of a warship in a situation like that - it refused to do so.

"Those shots weren't directed at the ship itself, they were directed as warning shots."