Japanese Prime Minister Junichiro Koizumi plans to introduce a bill to parliament that would allow women to take the throne.

Existing rules that permit only men to become emperors are proving problematic for the royal family as no boys have been born into the imperial family for 40 years, reports BBC News.

Koizumi said in an annual keynote speech that changes were necessary "in order that the imperial throne be continued into the future in a stable manner".

Last year a government panel recommended that women be allowed to ascend to the Chrysanthemum Throne.

If the bill is approved, it would allow Emperor Akihito's four-year-old grand-daughter, Aiko, to become second in line to the throne after her father, Crown Prince Naruhito.

Aiko is Crown Prince Naruhito and his wife Masako's only son. Pressure to produce a male heir caused her to suffer a stress-related illness and has led to her withdrawal from public life, reports BBC News.

According to opinion polls in Japan, most people believe that women should be allowed on the throne.