The United States believed in 1977 that nuclear weapons could be produced from plutonium extracted from spent nuclear fuel at Japan's light water reactors and conveyed its view to Tokyo, according to Japanese diplomatic records declassified Wednesday.

A U.S. arms control official told a Japanese diplomat based in Austria that the common belief that reactor-grade plutonium is unfit for weapons production is wrong, according to a cable sent by then-Ambassador to the U.S. Fumihiko Togo to the Foreign Ministry in Tokyo on Feb. 23, 1977.

At the time, the administration of U.S. President Jimmy Carter was pursuing nonproliferation following a nuclear test carried out by India in 1974.