Prime Minister Shigeru Ishiba is expected to secure enough support to be reelected in parliament despite the election setback after executives of smaller opposition parties announced Thursday that they will not support the country's main opposition leader's bid for the premiership.

The ruling Liberal Democratic Party and the main opposition Constitutional Democratic Party of Japan are eager to win the support of smaller opposition parties ahead of next month's parliamentary vote to select the new prime minister, as neither holds a majority in the lower house following Sunday's general election.

The secretary general of the Democratic Party for the People told his LDP counterpart on Thursday that the small opposition party, which saw its seats quadruple in the weekend election, will vote for its leader, Yuichiro Tamaki, during a special parliamentary session, likely starting Nov 11, to select the next prime minister.

The Japan Innovation Party, the second-largest opposition, is also unlikely to vote for the CDPJ chief Yoshihiko Noda, a party executive said.

For either Ishiba or Noda to be elected prime minister, they must secure majority support. If neither achieves this threshold, the vote will proceed to a runoff, where the candidate with the most votes will be appointed to the position.

The coalition of the LDP and the Komeito party has 215 seats, 18 short of the majority line of 233 in the powerful House of Representatives, while the CDPJ has 148. The DPP won 28 and the JIP 38.

The DPP told the LDP in the secretary general meeting that it will vote for Tamaki in all votes, which would benefit the ruling party if Ishiba and Noda compete in a runoff.

Japan was plunged into political uncertainty after the ruling bloc's crushing defeat, less than a month after Ishiba took office.

The LDP and the DPP are exploring ways to promote policy coordination.

LDP Secretary General Hiroshi Moriyama called on his DPP counterpart Kazuya Shimba to work together to craft a draft supplementary budget for fiscal 2024 to fund inflation relief measures and an initial budget plan for the next fiscal year from April.

While Moriyama proposed setting up a committee to be joined by policy chiefs of both parties for coordination, Shimba said his party would deal with measures on a case-by-case basis, the DPP No. 2 told reporters.

DPP leader Tamaki has advocated boosting people's incomes by raising the salary threshold for paying taxes. However, the government remains reluctant to introduce the step for fear of a possible decrease in tax revenue.

Moriyama told reporters that Shimba said the DPP will positively consider accepting a proposal to hold a meeting between Ishiba and Tamaki.

Ishiba is also scheduled to sit down with JIP leader Nobuyuki Baba next week, according to party officials.

CDPJ chief Noda, who was Japan's prime minister for over a year to December 2012 under the party's predecessor, is also rallying support. "Realistically speaking, it will be difficult to secure the nomination," he told a TV program.