Japan's main opposition, the Democratic Party of Japan (DPJ), on Wednesday deliberated over whether to expel ex-Prime Minister Naoto Kan from the party for supporting an independent candidate in Tokyo electoral district in upper house race, in defiance of party policy.

The party, headed by Banri Kaieda, discussed Kan's dismissal but failed to reach an agreement, though Kan's actions were widely believed to have contributed to the DPJ's crushing defeat in Sunday's upper house elections.

The elections saw the ruling Liberal Democratic Party (LDP) bloc sweep to a convincing victory and along with their smaller New Komeito Party ally, consolidate their power in both houses of parliament, with current Prime Minister Shinzo Abe fulfilling his campaign objective of ending a divided Diet.

Kan is at odds with his party for supporting single-term upper house lawmaker Masako Okawara, despite the lack of DPJ's backing for his endorsement, which made just two days before the election campaign kicked off.

Kan, known as a staunch anti-nuclear advocate following the earthquake-triggered nuclear disaster when he was prime minister two years ago, opted to defy his party and support Okawara as he believed the candidate's ideology was "more in line with party's stance to seek a nuclear phase-out by 2030s."

But Kaieda said that Kan and other senior party members' actions of late had detrimentally affected the DPJ election results on Sunday.

"Many party members said ex-Prime Minister Naoto Kan... negatively impacted the election results and called for severe punishment," Kaieda was quoted as saying at the start of the meeting to party officials Wednesday.

"We take the outcome seriously, and continue to work hard so our party can be rebuilt step by step," Kaieda said.

Following the DPJ's historic loss in Sunday's election, DPJ Secretary General Goshi Hosono announced his plans to tender his resignation next month to account for the crushing defeat.

Kaieda and Hosono agreed at the meeting that further discussions were needed on how to discipline Kan and another meeting would be held to tackle the matter.

Kan, for his part, conceded that he had "caused trouble" to the DPJ, but maintained that he "has no intentions of leaving the party of his own volition."

He said d that he will follow the party's decision, once it's made.

Following the election, Kan's candidate of choice Okawara and the DPJ failed to hold onto a seat in the Tokyo electoral district, which it held since 1998.

Kan stepped down as prime minister in 2011 following intense criticism regarding his mishandling of the earthquake-triggered nuclear crisis at a nuclear power plant in Fukushima Prefecture.