Yukio Hatoyama, leader of the Democratic Party of Japan, criticized Prime Minister Yoshiro Mori on Thursday for attending a wedding in 1995 at which a gang boss was present.
"If this is true, it is a big problem," Hatoyama said at a lecture at the Foreign Correspondents Club of Japan. "We have already branded him as inappropriate as a prime minister, but I think this will serve to reinforce that."
The chief of Japan's largest opposition party said the DPJ would carry out its own investigation into the matter.