Twenty-five gangs control Ireland's criminal underworld, a fifth of them with key international links, Garda Commissioner Martin Callinan has said.
The state's most senior police officer said five groups have a "significant international dimension" with tentacles spreading into Holland, Spain and the UK, countries which provide established routes for importing drugs into Ireland.
Intelligence shows Irish gangs are also forging associations with Russian gangs, particularly on cigarette smuggling as well as drugs ventures. "The presence of Russian organised crime groups operating in Spain is also influencing the activities of Irish criminals there," said Mr Callinan.
Gardai are working with international law enforcement agency Interpol to monitor these groups.
Mr Callinan said at the heart of each organised crime gang is a core of around six to 12 leaders who oversee middle managers, who in turn control low-level criminals who carry out the day-to-day activities.
The majority of gangs are centred in the large urban areas - Limerick, Cork, Galway, Sligo and Dublin - and there is a lot of interaction between them, including on joint enterprises such as drug importation.
While the overwhelming majority of the gangsters are involved almost exclusively in drug trafficking, they also engage in other activities like cash-in-transit robberies, firearms offences and "upper end" burglaries to fund major drug deals.
Speaking before an Oireachtas committee on justice about gangland crime, Mr Callinan told TDs and senators there was close co-operation between gangs in Ireland and Northern Ireland. The cross-border links help them trade in weapons and drugs, as well as counterfeit cigarettes, fuel laundering and stolen goods.
Detectives have "serious concern" about a "friction and facilitation" relationship between crime gangs and dissident republicans, who have been taxing some drug dealers in recent years, Mr Callinan said.
They also remain worried about the continued increase in cannabis factories, or grow houses, around the state. Mr Callinan said the operations provided a very quick turnaround in harvesting the drug, leading to a "conveyor belt of money" to organised crime gangs.