Defense Minister Taro Kono on Tuesday warned of risks in keeping the current imperial succession system in place that allows only male descendants in the family's paternal line to ascend to the throne.
Speaking at a news conference, Kono said it would be "extremely risky" for the current imperial family to maintain the male-line succession system.
He indicated that national debate should be initiated immediately on possible ways to ensure stable imperial succession, including allowing female emperors or emperors from the maternal bloodline and restoring the imperial family status to those who left the family soon after the end of World War II.
"Maintaining the male-line imperial succession system is the most desirable option," Kono said.
The minister, however, said that the country should also consider an option of allowing female members to remain in the imperial family after marriage as heads of family branches and have their children ascend to the throne, or possibly reinstate former male imperial family members or have them ascend to the throne through adoption.
"The emperor's status is based on the consensus of the people," Kono said, adding that the succession issue needs to be discussed by the public as soon as possible.
Emperor Naruhito and Empress Masako have one child, 18-year-old Princess Aiko. Prince Hisahito, the 13-year-old nephew of the emperor, is the only grandson of Naruhito's father, Emperor Emeritus Akihito.