Prime Minister Shinzo Abe says his ruling party must win next month's upper house elections to ensure a stable future for Japan after years of indecisive politics hampered by a divided parliament.

Speaking at a news conference Wednesday, Abe said his economic policies have totally changed Japan's mood since he took office six months ago following the Liberal Democratic Party's sweeping election victory in the more powerful lower house.

He said it was time to "bring an end to the twisted parliament" through the upcoming elections, and to "break new ground for Japan's future under a stable government."

The opposition's control of the upper house, where half the 242 seats will be up for grabs in elections planned for July 21, has made it hard to pass legislation.