The nation's two largest opposition parties agreed Friday to start discussing common ground with a view to fighting the Upper House election next summer with a united front.

Observers say the parties' aim to coordinate at least some of their policies could lead to a merger.

Katsuya Okada, president of the Democratic Party of Japan, the largest opposition force, and Ishin no To (Japan Innovation Party) leader Yorihisa Matsuno met at the Diet building for the talks and sounded upbeat in comments to reporters.