The Japanese Imperial Household Agency reportedly has a significant number of royal documents from the Joseon Dynasty in addition to the "Joseon Wangsil Uigwe."

The Cultural Heritage Administration of Korea said Monday that its field study of Korean cultural assets abroad found that 375 volumes of royal documents in 38 fields published toward the end of the Joseon Dynasty, are housed in the Japanese agency.

In addition, the agency has an additional 17 books, which were used to instruct kings.

The administration believes that officials of the Japanese colonial government took the documents secretly and donated them to the agency later, citing personal seals on the documents.

The administration said it will launch preparations for the return of the documents in cooperation with the South Korean culture and foreign ministries.

The Joseon Wangsil Uigwe, a meticulous record of royal ceremonies and rituals, was taken by the Japanese colonial government in 1922.

The collection was registered with the UNESCO’s Memory of the World registry in 2007.