China on Wednesday dismissed claims that the Diaoyu Islands were historically part of the Ryukyu chain, reaffirming its sovereignty over the islands.

Academics have long paid attention to the history of Okinawa and Ryukyu, the Diaoyu Islands are China's inherent territory, and have never been part of Ryukyu or Okinawa, foreign ministry spokeswoman Hua Chunying said.

Also on Wednesday, two scholars at the Chinese Academy of Social Sciences wrote an article in the People's Daily in which they offered concrete historical materials to prove that Diaoyu was not among the islands ceded to Japan by the Qing Dynasty (1644-1911) in the late 19th century.

The two scholars also called into question Japan's claim over the Ryukyu island chain, which includes Okinawa.

"History's unresolved questions relating to the Ryukyu have reached a time for reconsideration," they wrote.

Okinawa is the biggest of the Ryukyu Islands, which were once an independent kingdom and a vassal state of China before they were absorbed by Japan in 1879. After the end of World War II, the US began to build military bases and station troops in Okinawa, which now is a symbol of the US-Japan security alliance although local residents have been strongly protesting such activities.

The article came as Beijing and Tokyo are still at loggerheads over the Diaoyu Islands and tensions between them escalated further last month after a record number of Japanese Cabinet officials and lawmakers visited the Yasukuni Shrine, where convicted World War II criminals were honored.

China on Tuesday also urged the US to abide by its pledge to not take sides in the islands disputes after the Pentagon claimed in a report that Beijing's act of drawing straight baseline claims around Diaoyu is inconsistent with international law.

It is likely that Japan could step up its provocation against China over the dispute, especially after the US has sent a signal that it would be on the side of Japan, said Li Jie, a Chinese navy military expert, adding that frictions still cannot be ruled out in the area.

Agencies contributed to this story