Though Mr Ozawa has repeatedly denied knowledge of any murky transactions, he was forced to resign from a high-ranking position in the DPJ in June partly because the scandal was damaging the government's popularity.

ECONOMIST: Japan��s leadership challenge

Ms Wong decided to announce the news earlier this week because she acknowledged there would be interest from the public as a result of her high-ranking position within the government and because she wanted to protect her pregnant partner from any undue publicity.

BBC: Penny Wong: Australia's non-story of the week