The Greek culture ministry announced on Wednesday that it has asked Christie’s auction house in London to withdraw a 4th century B.C. funerary stele from a future auction, as it is believed that the artifact was exported illegally from Greece.

According to the announcement, the ministry systematically monitors auctions of cultural artifacts and, when there is legal proof that an item has been exported illegally from its country of origin, it takes all necessary measures to prevent its sale.

The ministry is now awaiting Christie’s reply to a letter on the issue.