TOKYO (REUTERS) - The 100-year-old uncle of Japanese Emperor Akihito, Prince Mikasa, died on Thursday, leaving only four heirs to the Chrysanthemum throne, the Imperial Household Agency said.

Mikasa's death coincides with renewed attention to the future of the ageing and shrinking imperial family and whether women should be allowed to inherit the throne, breaking a males-only succession tradition that conservatives say is central to an imperial tradition stretching back 2,600 years.

Mikasa was the youngest brother of the current emperor's father, Hirohito, in whose name Japan fought World War Two The prince, a scholar of ancient Oriental history, taught at colleges, and served as honorary president of the Middle Eastern Culture Center in Japan and the Japan-Turkey Society.

Emperor Akihito, 82, hinted in August that he wanted to abdicate - a step unprecedented in modern Japan and not possible under current law. The remaining four male heirs include 10-year-old Prince Hisahito, the emperor's only grandson.

The three older heirs are Akihito's 80-year-old brother and his two middle-aged sons including Crown Prince Naruhito.