TOKYO - JAPAN'S longest-serving prime minister - a Nobel Peace laureate - asked the US in 1965 to deploy nuclear weapons against China if war broke out between the Asian rivals, according to newly declassified government files obtained by Kyodo news agency.

During his first trip to Washington as the Japanese leader, Eisaku Sato told then-US Defense Secretary Robert McNamara that American military forces could launch a nuclear attack on China by sea if needed, Kyodo said on Monday.

Under its post-World War II constitution, Japan renounces war as a sovereign right and prohibits the use of force in international conflicts.

But the new details of Mr Sato's discussions with the US reveal a more complicated picture behind his strong public stance against nuclear weapons as well as his intense distrust of China.

His comments came a day after his talks with President Lyndon Johnson on Jan 12, 1965, during which he sought to reconfirm a US promise to defend Japan under the US-Japan security treaty, according to Kyodo. The documents show that Mr Johnson assured the Japanese leader of Washington's commitment to the pact.

China triggered Japanese and US concerns about the country's emergence as a nuclear power after Beijing tested its first atomic bomb on Oct 16, 1964.

Mr Sato, in office from 1964 to 1972, also told Mr McNamara that although Japan was technically capable of building atomic weapons, it had no intention of doing so, according to documents that were routinely declassified by Japan's foreign ministry after 30 years and obtained by Kyodo.

China's Ministry of Foreign Affairs did not immediately respond to a request on Sunday for comment.

It was Mr Sato who introduced in 1967 Japan's 'Three Non-Nuclear Principles,' which has guided the country's nuclear policy since then.

The resolution, approved by parliament in 1971, states that Japan will not own or make nuclear weapons, nor permit them into Japanese territory. Japan also joined the Nuclear Nonproliferation Treaty under Sato's watch.

His efforts were recognised by the Nobel committee in 1974, when he shared the peace prize with Irish human rights crusader Sean MacBride.

But Mr Sato's attitude toward the Chinese was frosty at best.

Japan and China never established diplomatic relations during Mr Sato's eight years in office, with Tokyo calling for Beijing to first recognise Taiwan.

Japan is the only country to have undergone a nuclear attack. The US dropped separate atomic bombs on Hiroshima and Nagasaki in the waning days of World War II.

The current US-Japan security treaty, signed in 1960, obligates both countries to 'maintain and develop' their ability to defend against armed aggression and to cooperate if Japan came under attack.

The agreement takes into account Japan's constitutional inability to help defend the US. -- AP