By Daniel Schweimler
BBC News, Buenos Aires
Argentine authorities have found 12 secret runways used for importing drugs from Bolivia and Paraguay, and arrested five people, including two policemen.
Investigators are now trying to trace the owners of the land and to arrest more officers implicated in the ring.
The investigation was sparked by a confession from one of the smugglers.
The authorities recorded conversations between the smugglers and local police in Santiago del Estero province, north-west of Buenos Aires.
The runways, up to 700m long (700 yards), were used by small planes, each carrying up to 500kg (1,100lbs) of illegal drugs, officials say.
Local police were recorded giving advice to the smugglers on weather conditions and the whereabouts of the federal authorities.
They are also thought to have helped in distributing the drugs to provinces in the north and west of Argentina and to Buenos Aires.
The investigation is continuing to find out who made the runways - no easy task, since the land they were built on was rented to third parties using false names.
The policemen arrested said higher-ranking officers were involved in the operation.
The planes could land undetected since there is little in the way of any kind of radar system in some of the remoter parts of Argentina - a subject being tackled by the defence ministry.