KEY POINTS:
Spain has formally laid claim to a shipwreck that yielded a US$500 million ($646.4 million) treasure, saying it has proof the vessel was Spanish and demanding the return of the booty recovered last year by a US deep-sea exploration firm.
Odyssey Marine Exploration had announced last May that it had discovered the wreck of the Nuestra Senora de las Mercedes - a Spanish warship sunk by the British Navy southwest of Portugal in 1804 - in the Atlantic.
It carried a cargo of 500,000 silver coins and other artefacts.
