The government secretly considered the option of allowing women to ascend the Imperial Throne from 1997, before officially starting a debate on the issue under a panel of experts in 2005, internal documents and other sources showed Thursday.

While the plan was later dropped, the confidential talks helped lay the groundwork for the government of Prime Minister Junichiro Koizumi, who served between 2001 and 2006, to lean toward revising the Imperial House Law, which allows only male heirs who have emperors on their father's side to reign.

The secret meetings started in 1997 under then-Prime Minister Ryutaro Hashimoto and were attended by government members such as Deputy Chief Cabinet Secretary Teijiro Furukawa. At that time, Emperor Akihito had no grandson.