Has Japan reneged on 1970s Diaoyu pact?

This week marks the 40th anniversary of the establishment of diplomatic relations between China and Japan. However, relations are so bad that Beijing has "adjusted" the reception to celebrate the occasion to "an appropriate time".

Originally, Tang Jiaxuan, president of the China-Japan Friendship Association and a former state councillor, was to host a banquet in Beijing tonight to mark the occasion. But that has now been cancelled.

The present crisis was precipitated by the Japanese government's decision to buy three of the Senkaku/Diaoyu Islands from their private Japanese owner, in an attempt, it was said, to prevent the right-wing governor of Tokyo from acquiring them.

From China's standpoint, the purchase marked the violation of a tacit understanding between the two governments going back to 1972. As Xinhua explained: "During the negotiations on normalisation of China-Japan relations in 1972 and on the signing of the Sino-Japanese Treaty of Peace and Friendship in 1978, the then leaders of the two countries, acting in the larger interest of China-Japan relations, reached an important understanding and common ground on 'leaving the issue of the Diaoyu islands to be resolved later'."

Deng Xiaoping proposed shelving the sovereignty issue in favour of joint development of economic resources.

Japanese officials today, however, insist that there was no agreement to shelve the dispute. In fact, from Prime Minister Yoshihiko Noda on down, they insist that "there is no territorial dispute".

However, Yohei Kono, former speaker of the House of Representatives, told the Japanese monthly magazine Sekai that Japan and China had agreed to maintain the status quo on the disputed islands. He called on the Japanese government to "make proper gestures or release appropriate information".

This injunction to "release appropriate information" is equally applicable to the Chinese side. If there are documents that show that leaders of the two countries agreed in the 1970s to shelve the issue, now is the time to make them public.

After all, since Japan denies that there was any such accord, it cannot accuse China of violating diplomatic protocol if documents are released.

In the early 1970s, China was isolated and keen to obtain Japanese recognition, so it is understandable that Chinese leaders should be willing to put aside the dispute. The question is: did Japan's leaders also agree to do so? There is some evidence that they did.

Deng's words then were not challenged by the Japanese government. In 1980, then Japanese prime minister Masayoshi Ohira said that Japan was "ready to discuss with China possible oil exploration and development off the Senkaku islands". It would appear likely that the two sides had such an agreement.

The release of documents by Beijing that support the Chinese position would help to explain to the world why China has reacted so strongly to Japan's actions.

Frank Ching is a Hong Kong-based writer and commentator. frank.ching@scmp.com. Follow him on Twitter: @FrankChing1