The Foreign Ministry compiled a document in 1959 warning that making a declaration of not going nuclear could hamper Japan's flexibility in pursuing national security, eight years before the country declared its three nonnuclear principles, according to documents that were part of a series of diplomatic papers officially declassified Monday by the Foreign Ministry.

Prime Minister Eisaku Sato declared the three principles of not producing, possessing or allowing nuclear weapons in Japan in the Diet in December 1967, laying the foundation for what later became Japan's peace diplomacy.

Sato won the Nobel Peace Prize in 1974 for the declaration and his contributions to peace.