Uruguayan navy and customs officials said image scans showing hidden anomalies led to the find in a first container.

Further containers were being opened, the officials said, and if all four containers held the same quantity the seizure could amount to around 15 tons.

In a statement, Uruguay's navy described the seizure as the "greatest blow to drug trafficking in the history of our country."

The soy flour, destined for Lome, Togo, in western Africa, had been loaded last Tuesday at a ranch in the region of Soriano in southwestern Uruguay.

Suspects 'baited'

Uruguay's El Observador newspaper quoted Director of Customs Jaime Borgiana as saying that customs personnel were waiting for suspects who "got baited."

The AFP news agency reported that authorities had been questioning a soy company owner and truck drivers who brought the merchandise to the port of Montevideo for export.

Last August, 4.5 tons of cocaine from Uruguay were seized in Hamburg port after the arrival of a container ship. The street value was put at €1 billion ($1.1 billion).

That find comprised 4,200 packets stashed in 211 sports carry bags inside a container. That freight had been declared as soybeans.

In South America, Colombia, Peru and Bolivia are regarded as the largest producers of coca leaf, the primary ingredient in cocaine.

ipj/kl (AFP, dpa)