(AP) The Colombian navy has seized a 60-foot long submarine that likely was used to haul tons of cocaine out to sea for shipment to the United States, officials say.

No drugs were found when the fiberglass submarine was discovered Thursday about 30 miles from the Pacific Coast port of Buenaventura, but three people were arrested and two speedboats seized, said Adm. Guillermo Barrera, the navy's chief of operations.

Barrera said the submarine carried cocaine to speedboats in the Pacific Ocean for transportation to Central America and on to the United States.

Authorities say smuggling cocaine by sea has in recent years become the top method of transport, as radar systems have made it exceedingly difficult to smuggle drugs in small airplanes without being detected.

In a separate joint U.S.-Colombian operation Friday, the navy stopped a speedboat carrying three tons of cocaine about 1,000 miles west of Buenaventura. Five Colombians were arrested, said Adm. Jairo Pena, head of the navy's Pacific fleet.