The largest Japanese opposition party since the Prime Minister Shinzo Abe's administration formed in late 2012 was established on Sunday, eyeing confrontation with the Abe-led ruling bloc in the summer's upper house election.

The newly formed party Minshinto, or the Democratic Party, came through the merger of two major opposition parties of the Democratic Party of Japan and the Japan Innovation Party, with DPJ chief Katsuya Okada elected as the new party's leader.

Calling the form of the new party as historic, Okada said in his speech at the party's inauguration that freedom, coexistence and responsibility for the future are the inaugural philosophy with which they start the Minshinto.