A possible rival for the leadership of Prime Minister Shinzo Abe's ruling party is speaking out against his plans to expand the role of the Self-Defense Forces.

"To tell the truth, that's a question mark," Seiko Noda said in an interview on Wednesday, when asked whether she backs the bills to enable Japan to defend an ally under attack. "Lawmakers who are practically defense nerds are suddenly flinging these unfamiliar ideas at the public."

Noda, who's been mentioned as a candidate to become Japan's first female prime minister, is only the second senior Liberal Democratic Party lawmaker to criticize the legislation.