"National police officers boarded a fishing boat in the Atlantic ocean with more than three tonnes of cocaine in parcels," , a police statement said.
"The captain of the boat, who is a Korean national, and four crew members of Indonesian origin, were arrested" and a further 16 people were detained on land , it added.
Police officials contacted by AFP were unable to specify for the time being whether the captain was from South or North Korea.
The statement said the racket involved a "Venezuelan organisation" active in the northwestern Spanish region of Galicia, where most of the arrests were made in the raids, codenamed Operation Albatross.
Police carried out 10 raids in various locations and seized firearms, computers, documents and vehicles.
Spain is considered a major entry point for drugs into Europe from South America and elsewhere.
On May 6th police said they had seized 52 tonnes of hashish, a European record, at a warehouse in the southern city of Cordoba, and arrested three people.
In March they seized two tonnes of cocaine on another boat bound for Europe from Venezuela.
Spain seized nearly 21 tonnes of cocaine last year, 25 percent more than in the previous year and 326 tonnes of hashish, down 8.5 percent from 2011, Interior Minister Jorge Fernandez-Diaz said last month.
That represented 41 percent of the total amount of cocaine seized in Europe last year and 74 percent of the hashish, according to the minister.