Japan was inclined in the 1960s to support China’s bid to join the United Nations if Taiwan could retain its membership, despite Japan’s formal opposition to China becoming a member, according to Japanese diplomatic files declassified Sunday.

Since 1976, the Foreign Ministry has been declassifying 30-year-old files each year, except for ones it thinks will affect state security, diplomatic negotiations or privacy.

In July 1961, Foreign Minister Zentaro Kosaka told Nobusuke Kishi, prime minister from 1957 to July 1960, that a majority of U.N. members would probably support a proposal that both China and Taiwan should be given U.N. seats, one of the files says.

Kishi, in response, told Kosaka, who was in Prime Minister Hayato Ikeda’s Cabinet, “To conclude, I think a two-China setup would be the only solution.”

The document backs up another diplomatic file declassified in 1998 which says Ikeda was thinking that year about supporting China’s U.N. bid on condition Taiwan would retain its membership.

But both China and Taiwan rejected a “two-China” solution and in October 1971 China joined the U.N. and Taiwan was expelled. Since 1993 Taiwan has been campaigning to regain its U.N. seat.

Japan established diplomatic relations with China and severed its formal ties with Taiwan in September 1972.

Japan’s wavering stance over its ties with China and Taiwan affected its domestic politics in the 1960s, according to the declassified files.

A file dated March 1964 quotes a senior Taiwan official as telling a Japanese Foreign Ministry official that some figures from Japan’s ruling Liberal Democratic Party had urged Taiwan to threaten to sever diplomatic ties with Japan.

The Foreign Ministry official interpreted this as indicating a possible attempt to hurt or overturn the Ikeda government by the LDP’s pro-Taiwan figures, who were frustrated by the administration’s policy, which they thought was inclined to be pro-Beijing, according to the file.

At that time, Japan-Taiwan relations had been strained by two incidents in 1963 that were thought to represent the Ikeda administration’s pro-Beijing stance — the government’s granting of permission for a textile plant export to China and its deportation of a Chinese interpreter to China, not to Taiwan.

Japan and Taiwan mended their fences in July 1964, when Foreign Minister Masayoshi Ohira visited the island.

In July 1966, Prime Minister Eisaku Sato told a visiting Taiwan official that China had apparently been working on LDP members so that they would support Beijing, another file says.

When Sato visited Taiwan in September 1967, Japan and Taiwan were at odds over the content of the joint communique, according to a separate file.

Taiwan insisted the communique should stipulate that Generalissimo Chiang Kai-shek and Sato had agreed existing ties among Asia-Pacific nations should be reinforced further to bring about peace and stability there, it says.

Japan was reluctant because such cooperation could be interpreted as anti-China and thus upset Beijing, but finally conceded to Taiwan to allow the statement because it did not include the word “anticommunism,” the file says.

Sato is viewed as one of the pro-Taiwan figures who prevailed in Japanese political circles in the 1960s.

But pro-China forces became powerful after China joined the U.N. in 1971 and Sato was succeeded in July 1972 by Kakuei Tanaka, who had been advocating establishing ties with China.