Worried that Japanese officials might renege on a deal that allowed U.S. military ships to bring nuclear arms into the country, Washington pressed Tokyo to make good on the secret agreement in 1964, according to newly declassified U.S. documents.

The documents, made available at a time when investigations into the pact are under way under the new administration in Tokyo, show how then U.S. Ambassador to Japan Edwin Reischauer urged ruling party heavyweight Masayoshi Ohira to exert his influence.

As a result, Reischauer and Ohira met in late September 1964 and the United States apparently got what it was seeking. Ohira, who served as prime minister from 1978 to 1980, was at that time in a senior position in the Liberal Democratic Party after leaving the post of foreign minister in a Cabinet reshuffle two months earlier.