Prime Minister Shinzo Abe said Wednesday the upcoming Upper House election is first and foremost about seeking a voter mandate for "political stability," which he says he has brought into Japan's politics after years marked by rapid succession of different prime ministers.

Abe's remark came at the end of the Diet session, its closure all but ruling out the possibility of him dissolving the Lower House for a snap election to take place simultaneously with the Upper House poll — a political maneuver dubbed a "double election." On Wednesday the government formally determined that the Upper House election will take place July 21, preceded by campaigning that would kick off July 4.

"The biggest issue to be debated at the upcoming election is whether we want to accelerate reforms befitting a new era under political stability, or slide back into that era of chaos," Abe told a news conference in Tokyo.