Italian police have seized more than 4 tons of cocaine worth 1 billion euros ($1.13 billion) on the street and arrested dozens of people suspected of running a huge mafia drug trafficking ring, a police official said. A court in Reggio Calabria - a city on the toe of the Italian boot - had issued an arrest warrant for 34 people, including high-ranking members of several Calabrian mafia clans, for international drug trafficking, a statement said. All but two have been arrested, finance police Colonel Mario Palumbo told Reuters. Spanish officials were seeking four people as part of the same investigation. Italy's finance police, which has jurisdiction at ports and borders, led the investigation. The U.S. Drug Enforcement Administration (DEA) provided intelligence on suppliers and shipments from South America. "The investigation by the DEA in South America identified several suppliers who were protected by commanders of the Revolutionary Armed Forces of Colombia (FARC)," a statement said, referring to leftist guerrillas in a long-time conflict with Colombia's central government. Over the course of 18 months, more than four tonnes of cocaine were seized, of which three tonnes were found in Italian ports, Palumbo said. Rival mafia clans had joined together to import large amounts of the drug at wholesale prices. "They used mainly banks in offshore tax havens to pay for the drugs," he said, to throw investigators off the money trail. The cocaine was put in large duffel bags and hidden inside shipping containers, and the mobsters relied on employees of various ports - especially the Calabrian port of Gioia Tauro - to collect it, Palumbo said. The Calabrian mafia's role as one of Europe's biggest cocaine importers has made it the most powerful economic force in its impoverished home region in southern Italy, according to a report by Italian anti-mafia prosecutors earlier this year. The bustling narcotics business has propelled the Calabrian mob, known as the 'Ndrangheta, ahead of Sicily's more storied Cosa Nostra as Italy's most powerful organized crime group.