PORT-AU-PRINCE, Haiti -- A report from the UN cultural agency released Monday concludes that a shipwreck found off northern Haiti could not be the Santa Maria, the lost flagship from Christopher Columbus' first voyage to the Western Hemisphere, as a U.S. explorer had claimed.

UNESCO said a team of experts who explored the site at the request of the Haitian government determined the wreckage was from a more recent vessel for reasons that included the discovery of copper nails and spikes at the site. The Santa Maria would have used components of iron or wood, the agency said.

The report, which the agency said was conducted in a "neutral and scientific manner," found that it is possible the actual wreckage may be buried under what is now land because of heavy sedimentation from nearby rivers.

U.S. explorer Barry Clifford had announced in May that he believed that he may have found the Santa Maria near the city of Cap-Haitien in what would have been a major archaeological find. The ship struck a reef and was abandoned by Columbus in December 1492 and about two dozen crew members were left behind.

Last month, Haiti's culture minister told The Associated Press that preliminary research indicated that the ship was not the Santa Maria and Clifford said that he expected that the UNESCO report would raise doubts.

He stood by his claim Monday, calling the UNESCO report flawed because the agency's experts did not consult him or the photos and charts he and his associates made of the wreckage site.

Clifford also said the copper components could have been used on the Santa Maria or the material came from another shipwreck that cross-contaminated the site in an area where a number of ships are known to have sunk.

The explorer had reached his conclusion based on the location of the wreckage, the presence of the type of stones used for ballast in that era as well as a type of cannon that was there when he first took photos of the site but had apparently been looted when he returned this year.

"All of this information I would have made available to UNESCO and they never asked me for it," he said by phone from Provincetown, Massachusetts.

In its report, UNESCO faulted Clifford for announcing his findings in the media before officially informing the Haitian government of his intention to continue his research in the bay of Cap-Haitien. The explorer said he had a permit.