Analysts say deterioration in Sino-Japanese ties triggered by betrayal of understanding reached 40 years ago

There have been many ups and downs in the Sino-Japanese relationship since diplomatic ties were established 40 years ago today, but analysts say the Japanese government's recent purchase of three of the disputed Diaoyu Islands in the East China Sea has plunged relations to their lowest ebb since 1989.

Beijing indefinitely postponed anniversary celebrations because China's core national interests were violated by the purchase of the islands by the government of Japanese Prime Minister Yoshihiko Noda, mainland-based experts said.

"The current deterioration of bilateral ties between Beijing and Tokyo has been triggered by Noda's betrayal of a verbal diplomatic understanding which was made by the two countries' former leaders in 1972, when both sides resumed relations," said Professor Peng Xi , deputy director of Nanjing University's Institute of Japanese Studies.

"The understanding, in which both sides agreed that the Diaoyu Islands are a disputed area, has been the fundamental base, with Beijing and Tokyo promising to put aside their disputes."

The uninhabited islands are known as the Senkakus in Japan.

The understanding, reached by late premier Zhou Enlai and his Japanese counterpart Kakuei Tanaka, was endorsed by Mao Zedong in 1971, when both sides started discussing the possibility of restoring diplomatic and trade ties.

On September 29, 1972, following a visit to Beijing by Tanaka, Japan formally established bilateral relations with Beijing and ended ties with the Kuomintang government in Taipei. The normalisation of Sino-Japanese relations was seen as building on then United States president Richard Nixon's trip to Beijing in February of that year.