The ruling coalition may lose seats in the next general election, preventing it from pushing through legislation, the Liberal Democratic Party's former policy chief warned.

"It will be difficult for the ruling coalition to retain a two-thirds majority but we'll strive to keep a majority," Shoichi Nakagawa said in an interview last week in Tokyo.

The government's two-thirds majority in the Lower House has allowed it to override vetoes by the upper chamber. The coalition was forced to use the maneuver this year for the first time since 1951 after the opposition blocked antiterrorism and tax legislation.