A forthcoming collection of historical documents on Ryukyu has yet again proven that the Diaoyu Islands are an inherent territory of China.

The 32-book collection about the kingdom - a vassal state of China during the Ming and Qing dynasties until Japan formally annexed Ryukyu in 1879 and renamed it Okinawato - is part of a series of books published by Fudan University Press that aims to explore and research Chinese civilization and its influence on East Asia.

Han Jiegen, history scholar and senior editor of The Collection of Historical Documents on the Ryukyu Kingdom, shows the documents that once again prove China's sovereignty over the Diaoyu Islands, in Shanghai on Wednesday. Liu Chang / China Daily

The Collection of Historical Documents on the Ryukyu Kingdom will be available by the end of the year.

Previously, the university press published historical documents about Vietnam and South Korea.

This new collection embodies almost all of the historical materials and documents left by the kingdom that still exist. The period of its involvement with China spanned more than 1,200 years (AD 607-1875).

"Many Chinese historical records have already proved the fact that the Diaoyu Islands have been Chinese territories since ancient times, while the new collection, standing at 'the other' side, offers further historical proof that the islands belong to China," said Han Jiegen, a history scholar and senior editor of The Collection of Historical Documents on the Ryukyu Kingdom.

"One argument that the Japanese raised when claiming sovereignty over the Diaoyu Islands is that the Diaoyu Islands belong to Ryukyu," he said. "But historical documents showed that the Diaoyu Islands and its affiliated islands were never part of Ryukyu territory."

The Diaoyu Islands consist of Diaoyu Dao, Huangwei Yu, Chiwei Yu, Nanxiao Dao, Beixiao Dao, Nan Yu, Bei Yu, Fei Yu and other islands and reefs, and are located to the northeast of Taiwan.

Poems, essays and other historical materials from the kingdom showed that the Diaoyu Islands have long belonged to China, Han said.

These historical materials clearly demonstrate that the Diaoyu Islands belong to China and Kumijima Island belong to Ryukyu, with Hei Shui Gou (known as Okinawa Trough nowadays) between the Diaoyu Islands and Kumijima Island as the separating line.

"The Diaoyu Islands had a very important strategic position in transportation. If they belonged to Ryukyu, it must have been reflected in historical and geographical documents. But the fact is that it has not," he said.

Zhong Shan Shi Pu, an official historical record of Ryukyu, is another important historical document.

This book gives a full introduction to the kingdom's own islands and its affiliated islands, including their official and common names. But the Diaoyu Islands' name and related names were not shown in the document.

Another historical document, Liu Qiu Guo Jiu Jiwhich recorded the kingdom's history, geography, custom, economy and culture, does not mention the islands.

"The Diaoyu Islands are an inseparable part of Chinese territory. China enjoys indisputable sovereignty over the Diaoyu Islands. I believe more evidence will continue to come out in the future with historians' continuous research," said He Shensui, director of the university press.

Contact the writer at wanghongyi@chinadaily.com.cn