Gardai have smashed a guns-for-sale racket in which suspected former members of the Provisional IRA supplied firearms to a drug trafficking gang in north Dublin.

Officers believe the suppliers were linked more recently with the dissident republican group, the Continuity IRA, but were also heavily involved in criminal activities.

They think the gang, based in Co Louth, was selling guns to a drugs gang operating in the Coolock area on the northside of the capital.

The breakthrough in the garda investigation came on Thursday night when armed gardai stopped two cars in Castlebellingham and Haggardstown, outside Dundalk.

This followed a surveillance operation on several targeted figures.

Detectives recovered an old Webley revolver, which was loaded, as well as ammunition and some cash.

Two men from Dundalk were arrested and taken to the local garda station. A man and a woman from Coolock were brought to Carrickmacross station but were released without charge last night.

The two held in custody were questioned under section 30 of the Offences Against the State Act and can be held for a maximum of three days without charge.

The garda operation involved detectives from the Louth division and members of the Emergency Response Unit and the National Surveillance Unit.

Senior garda officers said last night they did not regard the Louth gang as major suppliers of firearms to Dublin-based drug dealers.

But they described the seizure and arrests as significant, as the incident meant that the gardai had severed a vital pipeline for weapons.

The operation is part of on-going garda inquiries involving the national bureau of criminal investigation, the Special Branch and the crime and intelligence section at garda headquarters into the supply of weapons to crime gangs and their connections with members of former or active paramilitary groups.

Inquiries are also being carried out to establish the initial source of the guns.

Some of the weapons seized by gardai from crime gangs in the past couple of years are known to have been smuggled into the country as "sweeteners" with drug shipments.

But other firearms have been sourced overseas by the renegade republican groups, who have been trying to build up their own arsenals since the Provisional IRA declared a ceasefire, and have developed contacts in central and eastern European states.

The Real IRA and the Continuity IRA managed to purchase a sizeable haul of explosives and weaponry in the Balkans in 1999. But a large portion of this shipment was recovered by gardai in a disused wine cellar on land at Herbertstown, near Stamullen, on the Dublin-Meath border.

The following year a joint security operation involving gardai and international agencies led to a big arms and explosives shipment seizure in the Croatian town of Dobranje, near the Adriatic resort of Split.