Negotiations between the Democratic Party and Kibo no To (Party of Hope) on forming an alliance in the Diet broke down Wednesday amid strong opposition from rank-and-file lawmakers on both sides, with many citing differences in security policy and stances toward revising the Constitution.

The move comes two days after the secretary-generals of the two parties exchanged a consensus document to establish a unified political force to challenge Prime Minister Shinzo Abe's government and the ruling Liberal Democratic Party-led coalition when the ordinary Diet session convenes Monday.

The Democratic Party leadership gave up on securing a consensus on the matter within the party Wednesday, having sought to gain approval for the alliance plan from its members in a meeting that started in the morning.