The minister, Jang Jong Nam, was seen this week wearing a fourth star on his uniform, South Korea's Yonhap news agency reported Friday.
Last week, he displayed only three stars while attending a science fair organized by the Korean People's Army.
Recent press reports hint at other changes in the North Korean military. Ri Yong Gil, the tactical director of the General Staff of the People's Army, has been seen with a fourth star, signaling he also has been promoted. However, Gen. Kim Kyok Sik, the top member of the general staff, was not mentioned in the press report and was not visible in photos.
Kim Yong Hyun, a professor of North Korean studies at Dongguk University, said the promotions may indicate North Korean leader Kim Jong Un may be strengthening his hold on the military by forcing officers appointed by his father to retire.