To China, Japan's move to "nationalise" the uninhabited Diaoyu/Senkaku islands at the centre of an increasingly heated tussle between them is akin to someone seizing possession of something whose legal ownership is still being disputed.

One party's action is sure to trigger a reaction from the other. It did.

Now, for the first time, China is challenging Japan's sovereignty over a group of islands which used to be called Ryukyu islands and which now make up Okinawa prefecture.

Like the Diaoyu islands, the Ryukyus also lie in the East China Sea, between Japan's Kyushu island and Taiwan.

On September 14, a commentary in the People's Liberation Army (PLA) Daily asserted that "even the Ryukyu islands do not belong to Japan, under international laws governing the post-World War II order".

The Ryukyu islands came under the United States' civil administration from 1945 until 1972, when the Americans handed over control to the Japanese.

The PLA Daily's commentary stopped short of saying that the Ryukyus belong to China. But Chinese historical records would appear to support such a claim.

The earliest records of the Ryukyu islands can be found in the Book of Sui, written in AD621 to record the history of the Sui Dynasty (AD581-617). The Ryukyus used to be a tributary state of China. The name Ryukyu, in fact, originates from Liuqiu, also spelt Liuchiu and Lewchew, a name the Chinese gave to the islands.

Ryukyu historical records showed that from 1383 onwards, its kings derived their mandate to rule the islands from the Chinese emperor. This continued for nearly five centuries until 1879, when Japan annexed the islands and called them Okinawa prefecture.

This is well documented in historical records, which is why when the US-led Allied powers held discussions on "restoring territories", referring to Chinese territories that Japan had taken by force, both the Ryukyus and Taiwan were included.

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History is on China's side in islands dispute