A British Royal Navy warship has seized three tonnes of cocaine in a raid on a Venezuelan fishing boat in the Atlantic Ocean, the navy said Saturday.

HMS Portland was on routine patrol Friday in the north of the ocean when crew members spotted a suspicious-looking vessel and dispatched a helicopter to inspect it more closely.

As the helicopter approached, crew members allegedly threw packages over the side, which were later recovered and found to contain 500 kilograms of cocaine.

Troops found another two-and-a-half tonnes of cocaine on board the ship, a Navy spokesman added.

The boat is now being escorted back to Venezuela where officials will decide on prosecutions.

HMS Portland's commanding officer, Commander Mike Utley, said: "This drugs bust is the icing on the cake for what has been an extremely successful deployment."