The U.S. Army tested biological weapons in Okinawa in the early 1960s, when the prefecture was still under U.S. rule, according to U.S. documents obtained by Kyodo News.

In the tests, conducted at least a dozen times between 1961 and 1962, rice blast fungus was released over paddies to see how it affected production, the documents made available by U.S. authorities showed.

Rice blast disease causes lesions to form on the plant, threatening the crop. The fungus, which is known to occur in 85 countries, is estimated to destroy enough rice to feed 60 million people a year.