The precondition for the election is DPJ leader Naoto Kan offers to resign following the approval of two key bills by August 19. Kan has cited parliamentary passage of the government bond issuance and renewable energy bills as a condition for his resignation.

The DPJ leader is almost certain to become Japan's next prime minister as the party controls the majority of the more powerful lower house.

Kan has been blamed for lack of efficiency in handling the March 11 quake and tsunami, which triggered a nuclear crisis in Fukushima. Opposition parties said his holding on to power hindered cross-party cooperation to revive the country's economy.

Japan's finance minister Yoshihiko Noda, industry minister Banri Kaieda are the front runners in the leadership race, while former foreign minister Seiji Maehara has reemerged as another potential candidate to succeed Kan.