Government papers declassified Thursday revealed a key speech by Prime Minister Eisaku Sato in 1965 in then-occupied Okinawa was revised under U.S. pressure to stress the importance of Washington's military presence in the region.

Sato was the first prime minister to visit since the war. During the trip, he signaled Tokyo's willingness to extend the bilateral security treaty beyond its minimum 10-year term, and which would otherwise have expired in 1970.

"The Ryukyu Islands are playing a very important role for peace and security of the Far East," Sato said, reading text inserted just before his visit in August that year.