A senior Japanese politician, viewed as a strong contender to become the country’s first female prime minister, has broken ranks within the ruling party and questioned new security legislation that would expand the role of the military.

Seiko Noda’s public expression of doubts over the plans, said analysts, highlights the increasing vulnerability of Prime Minister Shinzo Abe as he wrestles with falling approval ratings and flagging economic momentum.

Asked in an interview with Bloomberg whether she supported the security bills — which secured lower house approval earlier this month — Ms Noda, who served as chairwoman of the Liberal Democratic party’s general council earlier in her political career, said: “To tell the truth, that’s a question mark.”