A French judge is due to rule on Friday on whether an auction of American Indian masks can go ahead in Paris amid claims by the tribe that they were stolen.
Representatives of the Hopi people say the masks are for religious ceremonies only and want them returned.
Some 70 brightly-coloured masks made of leather, wood and rope are due to be sold off by a private French collector.
The US ambassador to France is reported to be “very concerned” about the sale, questioning whether it might be contrary to the 1970 Unesco convention on cultural property.
The auctioneer has argued that most were sold by the American Indians themselves over the past 30 years, insisting that the Hopi case has no legal basis under French law.