The UN is sending experts to Madagascar to assess a claim by underwater explorers that they have found treasure and the wreck of a ship belonging to the pirate known as Captain Kidd.

Ulrike Guerin, a specialist in underwater heritage for the UN cultural agency Unesco, said that experts will examine artefacts at the site where American explorer Barry Clifford had been operating. The team is expected to arrive in Madagascar by the end of June, she said.

Unesco is also concerned that Clifford’s group may have damaged the site, alleging the explorers did not have an archaeologist with proper qualifications and did not present a proper plan to Madagascar’s authorities before they started diving.

October Films, the London-based production company that was filming Clifford’s work in Madagascar for television, said in a statement that a detailed plan had been submitted to the government before diving and that a respected marine archaeologist was on hand at all times to supervise the exploration. It said artefacts discovered by Clifford were handed over to the government and that the expedition is funding the restoration of a local museum and a small laboratory to preserve the artefacts.

Last week, Clifford said he found a silver bar that he believes belonged to William Kidd, who raided ships in the late 17th century and was executed in London in 1701. Clifford presented the bar to Madagascar’s President, Hery Rajaonarimampianina, in a ceremony on the country’s Sainte Marie Island.

The island, a hideout for pirates when Kidd was active, offered safe harbours and was close to maritime trading routes.

Last year, Clifford said he found the wreck of the Santa Maria, the lost flagship from Christopher Columbus’s first voyage to the Western Hemisphere, during a search off the coast of Haiti. Unesco visited the site and said there was no way the wreck could be the Santa Maria because nails and pins they found there were made of a copper alloy, indicating the wreck was a more recent ship.