Three men are being questioned by gardaí following the seizure of 7kg of heroin with an estimated value of over a €1 million.
The men, who are aged in their 40s and 50s, were detained as part of a joint operation by the Garda's Drugs and Organised Crime Bureau and the UK's National Crime Agency into an international drugs importation network.
Gardaí had a number of people under surveillance as part of the investigation, including a Turkish man, suspected to be an international drugs importer and an Indian man, a convicted drug dealer who served a lengthy sentence in the UK.
They were stopped in a car on Saturday along with an Irish man who is well known in social circles.
The drugs were discovered in searches in Meath and Dublin.
The three men are being held at garda stations in Dublin.
Gardaí suspect the drugs were being brought in by a west Dublin-based gang led by two brothers, which has links to the Kinahan organised crime gang.
Gardaí said investigations are ongoing nationally and internationally.
Detective Chief Superintendent Angela Willis of the Garda National Drugs and Organised Crime Bureau said: "This substantial seizure of heroin will help keep our communities and people safe and will impact significantly on organised crime groups involved in the international drugs trade."
Assistant Commissioner John O'Driscoll of Special Crime Operations said: "This seizure of a large amount of heroin is the result of an intelligence led investigation.
"This demonstrates the increased capabilities of the Garda Síochána, when working with our international partners, to keep people safe and to target those who would attack our communities with drugs."