Employees of trading house Mitsui & Co. are being questioned on suspicion that they bribed a Mongolian government official last year to secure an order for a power project financed by the Japanese government, informed sources said Wednesday.

Employees of Tokyo-based Mitsui, including 39-year-old Yusuke Shimazaki, offered more than 1 million yen to a director general-level official overseeing electric power and energy management within Mongolia's Infrastructure Ministry, the sources said.

Shimazaki has already been indicted on suspicion of manipulating bids for a project on Kunashiri, one of the disputed Russian-held islands off Hokkaido, that was funded via official development assistance.