Police in Italy and six other European countries Monday arrested dozens of mafia suspects in an international anti-drugs sweep. Police said they seized six tonnes of cocaine and 10 million euros of assets during the raids.

The operation uncovered a "colossal" trafficking operation run by the Calabrian mafia from the northwestern Piedmont region, according to paramilitary Carabinieri police who conducted Monday's raids in Italy.

Police also identified Swiss bank accounts linked to the drug traffickers whose operation shipped cocaine to Europe from Venezuela, Argentina and the Dominican Republic aboard a "flotilla" of boats manned by Italian and foreign crews.

Local police also carried out anti-drugs raids in Bulgaria, Slovenia, Spain, the Netherlands, Finland and Croatia as part of Monday's operation.

The Calabrian mafia or 'Ndrangheta, Italy's most powerful mafia, controls the European cocaine trade and has links to South American drug cartels and criminal organisations in Canada, Australia and other parts of the world.

Italy's national anti-mafia directorate said in a March 2011 report that the 'Ndrangheta was continuing to expand and had 'colonised' the wealthy north of Italy owing to its 'unlimited financial resources'.