Egypt has requested help from Interpol to retrieve a bust of Tutankhamun that was sold at auction in London last week for over £4.7 million (€5.2 million).
A lawsuit in the UK has also been launched on behalf of Egypt.
In a statement released on Tuesday, Egypt's National Committee of Antiquities said it felt "deep dissatisfaction" at Christie's auction house for allegedly ignoring requests to postpone the sale.
The statement added that a "great surprise" was also felt at receiving less than expected support from British authorities upon the request.
Egyptian authorities campaigned to postpone the auction last Thursday amid claims the 28.5cm-high quartzite statue had been looted from Karnak Temple in Luxor.
But Christie's maintains that it had provided "extensive information" about the bust.
Speaking to the Guardian, the auction house said Egyptian officials had been invited to meet with their representatives to discuss the relevant documentation, but that the offer had not been taken up.
Egypt's antiquities committee says no such legitimate proof had been shown in the way of deeds or documents showing the artefact's legal departure from the country.
The 3,000-year-old bust was sold from the Resandro Collection, a private collection of Egyptian art that was sold in part in 2016 for more than £3m (€3.3m).
It depicts the ancient Egyptian god of the sun and air, Amun, with the facial features of ancient boy pharaoh Tutankhamun.
Ahead of last week's auction, Christie's released a statement saying it recognised that such objects "can raise complex discussions about the past", but that it would "continue to provide a transparent, legitimate marketplace upholding the highest standards for the transfer of objects."
It added: "There is an honourable market for ancient art and we believe it is in the public interest that works come out into the open with the opportunity for them to be researched, as well as seen and enjoyed by global audiences.”
Watch an interview with archaeologist Jens Notroff in the video above.