According to an inventory check of artwork at the State Museum of Art and Sculpture in Ankara, Turkey, there were over 300 art pieces that were discovered to have been stolen. Included in the missing artwork were items that were found to be replaced by counterfeits.
In a single art theft case in late 2013, security services in Turkey stated that up to $30 Million in artwork was taken from the state museum. Despite 30 major artworks being recovered from a operation in Istanbul, about 40 paintings are still missing from this one incident.
Source: AFP, “Turkey probes wave of museum art thefts,” Global Post, December 9, 2013.