Police who swooped on a Belfast hotel were part of an international operation against a crime boss connected to the murder of journalist Veronica Guerin.
The arrest in a city centre hotel was followed by a PSNI seizure of 14 Glock pistols at an undisclosed location, while gardai intercepted a significant haul of drugs and guns.
Dutch police have also been involved in the co-ordinated move against weapon and drug trafficking.
The mastermind of the foiled importation is believed to be Brian Meehan, who is serving a life sentence in the Republic for his role in the Guerin murder in June 1996.
The man arrested in Belfast is from the Republic and is being questioned by police at the Serious Crime Suite in Antrim.
Heavily armed Garda detectives also arrested a man, at a suspected drugs drop-off point in Dublin.
Twenty-seven firearms and a massive haul of drugs were seized in the Republic as part of the operation, which was carried out with the assistance of Dutch police.
Twenty kilos of heroin and 10 kilos of herbal cannabis, with an estimated street value of €4m (£3.25m), were recovered.
PSNI Detective Superintendent Essie Adair described yesterday’s seizures and arrests as “significant”.
“There are no paramilitary organisations involved — this is purely an organised criminal cartel,” he said. “This is a significant investigation and a significant success in combatting international organised crime.
“This was an intelligence-led operation which has been ongoing for some time against serious organised criminal gangs based in the Republic of Ireland.”
Det Supt Adair said that the individual arrested in Belfast was of interest to police “due to his international organised crime links”.
He would not comment on whether there had been any arrests in the Netherlands.
“The investigation has been ongoing for some time and has involved close liaison with colleagues in An Garda Siochana and the Dutch police service, as well as HMRC and Irish Revenue Commissioners,” he said.
Gardai Commissioner Fachtna Murphy said the arrests had damaged a powerful European drugs trafficking network.
“We believe that this operation has made significant inroads into an international organised crime gang involved on a large scale in the importation of drugs and firearms into Ireland and the United Kingdom. This extensive operation could not have been successfully concluded without absolute co-operation across all three jurisdictions,” he said.
The Republic’s Justice Minister Dermot Ahern praised the success of the operation and said it was “a highly significant capture of illegal drugs