The United Nations says it is sending experts to Madagascar to assess a claim by underwater explorers that they had 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 U.N. cultural agency UNESCO, said Thursday that experts will examine artefacts at the site where American explorer Barry Clifford had been operating.

UNESCO is also concerned that Clifford's group may have damaged the site.

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.