A private light aircraft used in the operation, which is believed to have been orchestrated by the Kinahan cartel, was also seized.
The plane confiscated by gardaí on Thursday is the second found this year by officers investigating drugs trafficking – another was taken in Waterford last February.
The Kinahan cartel are being described as the “controllers” behind what was one of the biggest cocaine seizures of the year.
Gardaí said the plane that landed at a Longford airfield had been under surveillance in an intelligence operation mounted by specialist detectives.
They believe it is “highly likely” the cartel had previously used airfields in rural parts of the country to smuggle in large quantities of drugs.
“This is very unlikely to be the first time that the cartel used this method of trafficking drugs into the country,” a source saidlast night.
“In fact, international investigations have shown that the Kinahan cartel are frequently using light aircraft at different locations, including in Africa, for smuggling drugs.”
The private plane used to transport €8.4m worth of cocaine into Ireland set out from a tiny airport in northern France on Thursday afternoon before landing at the remote Abbeyshrule Aerodrome in Co Longford.
Undercover gardaí were watching as the drugs were moved from the aircraft into a single vehicle that was then driven away with another car in convoy at about 5.30pm.
The two vehicles were monitored, and around half-an-hour later officers intercepted them on back roads in the Lough Owel area near Mullingar, Co Westmeath.
Two men, aged 54 and 40, were arrested. Both have addresses in Ireland – in Waterford city and in Naas, Co Kildare – and one of is said to be an eastern European.
They were still being questioned last night at Ashbourne garda station in Co Meath.
All the drugs were discovered in one car, where it was distributed between six holdalls and one large suitcase.
“The suspects were driving on back roads to avoid detection but were being monitored all the time,” a source said.
Hailing the success of the Operation Tara seizure, gardaí said more than €50m worth of drugs had now been seized during similar raids in Ireland so far this year.
A garda source said yesterday they had worked with international police partners as part of their investigation.
This is the latest major setback for the Kinahan cartel after cannabis valued at nearly €7m was seized in a separate operation last month.
A garda spokesperson said of Thursday’s raid in Longford:
“In the course of this operation, 120kg of cocaine with an estimated street value of €8.4m, subject to analysis, was recovered, along with several communications devices.
“Follow-up searches were conducted at residential premises in Naas, Co Kildare, and Waterford city, and at a commercial airfield in Co Longford where a light aircraft has been seized.
“Two males, age 54 and 40 years, were arrested on suspicion of drug trafficking contrary to section 15 of the Misuse of Drugs Act 1977 and are currently detained, pursuant to the provisions of section 2 of Criminal Justice (Drug Trafficking) Act, 1996.”
Following Thursday’s seizure, Assistant Garda Commissioner Justin Kelly, the head of the Organised and Serious Crime Unit, said: “This operation has prevented a considerable quantity of dangerous drugs from making it on to our streets and causing significant harm to our communities.
“An Garda Síochána is committed, under Operation Tara, to disrupting and dismantling the organised criminal networks who profit from drug trafficking and impact so negatively on our society.”
Earlier this week, the Irish Independentrevealed that the Kinahan cartel is continuing to operate multi-million-euro drug shipments despite sanctions being imposed on the leaders.
An investigation is trying to determine whether Spanish-based members of the cartel organised for the €8.4m worth of cocaine to be flown into Ireland after it was first brought to continental Europe from South America.