Story highlights U.N. experts say a wreck found off Haiti is not that of the long-lost Santa Maria

An American explorer said in May he believed he'd found Christopher Columbus' flagship

But UNESCO says that bronze or copper fasteners at the site indicate it was a later wreck

The Santa Maria foundered in 1492 as Columbus made his first voyage to the Americas

An American explorer's claim to have found the long-lost Santa Maria, Christopher Columbus' flagship from his first voyage to the Americas, has been dismissed by a group of U.N. experts.

Underwater explorer Barry Clifford made headlines when he said in May that he believed a shipwreck on a reef off Haiti's northern coast could be the fabled ship, which went down in 1492.

But a team from the U.N. cultural agency UNESCO said in a report Monday that bronze or copper fasteners found at the site point to shipbuilding techniques of the late 17th or 18th centuries, when ships were covered in copper. Before that, fasteners were made only of wood or iron, it said.

"There is now incontestable proof that the wreck is from a much later period," according to the report by mission leader Xavier Nieto Prieto, who visited the site for several days beginning September 9.

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The experts also believe that contemporary accounts, including Columbus' own journal, indicate that the wreck is too far from the shore to be that of the Santa Maria.

The UNESCO mission was requested by the Haitian government to check out Clifford's claim to have solved a 500-year-old mystery.

The Santa Maria was the flagship of Columbus' small fleet that set sail from Spain in August 1492 under the sponsorship of King Ferdinand II and Queen Isabella I.

The voyage aimed to find a westward route to China, India and the gold and spice islands of the East. But the land the sailors set eyes on in October 1492 was an island in the Caribbean.

Explorer Brandon Clifford believes these are the remains of Columbus' Santa Maria.

Among the islands on which Columbus set foot was Hispaniola, which is divided between Haiti and the Dominican Republic. Columbus established a fort in Haiti.

That December, the Santa Maria accidentally ran aground off the island's coast. Some planks and provisions from the wrecked ship, which was about 117 feet (36 meters) long, were used by the garrison at the fort, according to Encyclopaedia Britannica.

Columbus set off back to Spain with the two remaining ships, the Nina and the Pinta, in January 1493.

The UNESCO report called for further investigations to find the Santa Maria and urged Haiti to take steps to ensure that its underwater heritage is protected in line with U.N. conventions.