International campaigners are making last-minute efforts to halt the sale in Paris of sacred ceremonial masks and headdresses from Native American tribes.
The US embassy appealed to the auction house to delay the sale, due to be held on Monday and Tuesday, so the 25 items from the Hopi and San Carlos Apache tribes can be identified to see whether they can reclaim them.
The battle follows attempts to halt an auction of 70 Hopi masks in Paris in April. Even the intervention of the Hollywood actor Robert Redford, who described the earlier sale as a "criminal act … that could have serious moral consequences", was not enough to halt the €930,000 (£780,000) sale.
On Friday, Survival International, which campaigns for the rights of indigenous peoples, lost a legal challenge over the latest auction. The French judge, Claire David, said neither moral nor philosophical considerations could justify preventing a legal sale.
On Saturday, Mark Taplin, the US charge d'affaires in Paris, delivered a letter to the EVE auction house asking for the sale to be delayed.
"The embassy made this request on behalf of the two tribes so that they might have the opportunity to identify the objects, investigate their provenance and determine whether they have a claim to recover the items under the 1970 Unesco convention on the export and transfer of ownership of cultural property, to which France is a signatory, or under other laws," the embassy said in a statement.
US diplomats emphasised the "great importance" of the objects to the Native Americans and said they should not be sold "precipitously and in the absence of consultation" with the two tribes.
The sale of sacred Native American artefacts was banned in the US in 1990 but there is no similar legislation in France.
The EVE auction will sell more than 100 Amerindian artefacts, but the rare masks, described as "exceptional" are the most contested. Among them, is a version of the Tumas Crow Mother mask dating from the 1860s and given a catalogue price of between €60,000 and €80,000.
EVE auctioneer Alain Leroy said: "Never has a sale of Amerindian art gathered together as many ancient and rare objects."
