The United Nations cultural agency has called on Colombia not to commercially exploit the 300-year-old wreck of the Spanish galleon San Jose, which is believed to contain a cargo worth billions of pounds.
A Unesco experts' body protecting underwater cultural heritage sent a letter to Colombian culture minister Mariana Garces Cordoba expressing concern that recovering the treasure for sale rather than for its historical value "would cause the irretrievable loss of significant heritage".
The letter was made available by the body's head, Auron Tare.
"Allowing the commercial exploitation of Colombia's cultural heritage goes against the best scientific standards and international ethical principles as laid down especially in the Unesco Underwater Cultural Heritage Convention," the letter said.
"The San Jose shipwreck represent cultural heritage," it said, adding Unesco would be ready to offer its expertise.
Colombia has not signed the UN Convention on the Law of the Sea, which would subject it to international standards and require it to inform Unesco of its plans for the wreck.
Colombian authorities intend to recover the San Jose, ending a three-century saga since June 8 1708, when the ship sank with 600 people aboard while trying to outrun a fleet of British warships.
It is believed to have been carrying 11 million gold and silver coins, emeralds and other precious cargo from Spanish-controlled colonies, which could be worth billions if recovered.
The wreck was discovered three years ago with the help of an international team of experts and autonomous underwater vehicles, and its exact location is a state secret.
The ship sank somewhere in the wide area off Colombia's Baru peninsula, south of Cartagena, in the Caribbean Sea.
The vessel, which maritime experts consider the holy grail of Spanish colonial shipwrecks, has also been the subject of a legal battle in the US, Colombia and Spain over who owns the rights to the sunken treasure.
Unesco experts have complained of "a constant disregard of best archaeological standards" from treasure hunters dealing with the San Jose.
Mr Tare said they had learned that "the recovery of artefacts from the Spanish galleon San Jose will be held contrary to the Unesco convention, not in a scientific, ethical way and for commercial profit of a third party".
The three-decked San Jose was reportedly 150ft long, with a beam of 45ft and armed with 64 guns.
Colombia has said that researchers found bronze cannons that are in good condition, along with ceramic and porcelain vases and personal weapons.
The researchers say the specifications of the cannons leave no doubt that the wreck is the San Jose.