Indonesian President Sukarno asked Prime Minister Hayato Ikeda in 1964 to send a mission to monitor a ceasefire between Indonesia and Malaysia.
Diplomatic documents recently declassified show that Japan was asked to contribute to peacekeeping less than 20 years after its surrender in World War II.
Indonesia, which opposed the independence of Malaysia in 1963, had sent guerrillas to infiltrate northern Borneo Island, part of Malaysian territory, where they clashed with British forces stationed there.