Yukio Edano, senior member of the moribund main opposition Democratic Party, announced Monday the establishment of a new political group with liberal members whose stances are at odds with a new force formed by Tokyo Gov. Yuriko Koike ahead of an upcoming lower house election.

Democratic Party President Seiji Maehara has decided to effectively disband his party and let its members run in the Oct. 22 general election with Koike's Kibo no To (party of hope) in a bid to unite voters against the administration of Prime Minister Shinzo Abe.

But Koike, a former lawmaker of Abe's Liberal Democratic Party, has said her "reform-minded conservative" party would not accept all of them and that new entrants will be required to share views on national security and amendment to the Constitution, indicating liberal-wing Democratic Party members will likely be excluded.

In Japanese politics, "liberal" typically refers to supporters of the postwar pacifist Constitution.

Edano, the deputy head of the Democratic Party who was defeated by Maehara in a leadership race in September, has said it is "necessary to form a party -- the Constitutional Democratic Party of Japan -- for former lower house members who would not be able to join Kibo no To," according to sources close to the matter.

In addition to Edano, vice president Shoichi Kondo, Akira Nagatsuma, who chairs the party's election campaign committee, and Hirotaka Akamatsu, a former vice speaker of the lower house, are expected to join Edano's party, the sources said.

Edano's move could prove a setback to the opposition's attempt to form a united front against Abe's government, raising the possibility of a three-way battle between the ruling coalition, Koike's party and a more liberal force led by Edano.

Former Prime Minister Yoshihiko Noda of the Democratic Party told reporters he will run as an independent, saying he is "a moderate conservative." Katsuya Okada, another party heavyweight who served as deputy prime minister, and Jun Azumi, a former deputy president of the party, will follow suit.

Noda made the comments after Goshi Hosono, one of the founding members of Kibo no To who had left the Democratic Party, said he wanted "those with experience of leading one of the three branches of government" to refrain from joining the party.

Hosono's remarks apparently reflect Kibo no To's aim to erase any negative image associated with the administration of the Democratic Party's predecessor, the Democratic Party of Japan, between 2009 and 2012.

A total of 465 seats will be up for grabs in the upcoming House of Representatives election as the number will be cut from 475. The ruling coalition of the LDP and Komeito party held more than 300 seats in the lower house before the chamber was dissolved last week.

Kibo no To is expected to announce later this week its candidates' list consisting of around 200 contestants, more than half of whom are from the Democratic Party, according to the party sources.