The FBI is investigating the sale to US buyers of what are suspected to be hundreds of treasures from the British Museum.
The BBC understands the US law enforcement agency has also assisted with the return of 268 items, which the museum claims belong to it, that were sold to a collector in Washington DC.
The British Museum announced last year that ancient gems, jewellery and other items from its collection, were missing, stolen or damaged.
One buyer, based in New Orleans, told the BBC an FBI agent had emailed him asking for information about two pieces he had bought on eBay.
The FBI agent said they were assisting the Metropolitan Police with investigating missing or stolen items from the museum.
The buyer has said he is no longer in possession of either gem and does not believe they have been located by authorities. The FBI did not request further information from him.
The British Museum says 626 items have so far been recovered of 1,500 it estimates are stolen or missing
The British Museum says of 1,500 items it estimates are stolen or missing, 626 have so far been recovered and 100 more have been found but not yet brought back.
The vast majority of items the museum believes to have been stolen were uncatalogued and it is still in the process of looking for ways to prove they come from its collection. In some cases, this involves collectors agreeing to donate items to the museum so staff can assess.
A senior curator, Peter Higgs, is accused by the British Museum of stealing, damaging, melting down, and selling ancient artefacts. He denies the allegations.
The museum has said it believes Dr Higgs pocketed an estimated £100,000 in total.
According to court documents in a civil case the museum is bringing against Dr Higgs, it believes he was stealing items for at least a decade, selling mostly unregistered items from the museum’s storerooms.
The museum believes Dr Higgs, who has been dismissed, had sold items to at least 45 buyers on eBay.
Dr Higgs is defending the civil claim against him.
Nobody has been arrested or charged with any offence.
<<BBC>>
