Twenty-eight Japanese have officially been recognized as falling ill from inhaling asbestos while working at U.S. military bases in Okinawa, including 21 who have died, Health, Labor and Welfare Ministry data showed Tuesday.

They represent more than half of the 48 people recognized with asbestos injuries in Okinawa. It is feared there could be more victims among people who have worked at military bases. An ex-worker said they were not provided adequate protective gear or informed of the dangers of asbestos.

Of the 28 workers, 19 were officially recognized in the period through fiscal 2012 as having suffered work-related asbestos hazards. Fourteen suffered lung cancer, nine of whom have died; three suffered asbestosis and have all died; and two suffered mesothelioma, a form of cancer.