Korea and Japan are unlikely to conclude this year an agreement on the transfer of ancient Korean books Japan took from the Korean Peninsula under colonial rule.

The Japanese daily Sankei Shimbun said Sunday that Tokyo planned to return the documents this year to mark the centennial anniversary of Japan’s annexation of the peninsula, which the paper said became impossible due to prolonged deliberation by the Japanese parliament.

The materials include royal documents from Korea's Joseon Dynasty.

The daily says Japan's Imperial Household Agency has yet to decide on the list of books to be returned.

Japanese Prime Minister Naoto Kan said in a statement in August that Tokyo will soon return ancient books and cultural assets that his country took from the Korean Peninsula in the colonial period.