MADRID, Spain (AP) _ Police have confiscated an estimated 10 tons of cocaine aboard a sailboat near Spain's Canary Islands and have arrested 54 people in what they say is the biggest single seizure of cocaine so far in Europe.

The seizure and arrest of 16 Russian crew members occurred Sunday, Javier Hernandez of the National Drug Control Agency said Wednesday.

Thirty-eight people have since been arrested in Spain in connection with the case, including a Colombian suspected of setting up the shipment, said National Police Chief Juan Contino.

The boat, flying a Caribbean flag, was sailing in international waters at the time and was scheduled to dock in Las Palmas, Canary Islands, on Friday. It is believed to have set out from an unspecified South American country, according to the El Pais newspaper.

Cotino told a press conference in Madrid that one of the boat's crew members died of a suspected heart attack suffered during Sunday's raid. He said the operation remained open and did not discount further arrests.

The operation, the result of months of investigations, was carried out by drug enforcement and customs agents and supervised by National Court Judge Baltasar Garzon.

Cotino said the arrested Colombian, identified as Alfonso Leon, was the link between Colombian drug cartels and Spanish drug gangs based in the northwestern region of Galicia.

Colombian traffickers have begun using Spanish gangs to channel drugs through the country to destinations elsewhere in Europe, Cotino said. The Spanish gangs are paid with a portion of the shipments, he said.

The paper said connections with gangs in Britain led authorities to suspect that part of the shipment was destined for England.

The biggest cocaine seizure in Europe prior to this one was a six-ton shipment in Naples in 1995, according to Italian authorities.