TOKYO A former Japanese prime minister joined the swelling ranks of ruling party rebels trying to oust leader Naoto Kan, raising the risk that a no-confidence vote will pass in parliament on Thursday, forcing him to quit.
Japan's fifth premier in as many years, Kan has come under fire for his handling of the nuclear crisis triggered by the March 11 earthquake, the world's worst in quarter of a century.
The Democratic Party of Japan (DPJ) rebels lining up against Kan also resent what they see as his high-handed style and fear his unpopularity and a policy shift toward fiscal reform could scuttle their chances if the opposition forces an election.
The opposition will need the votes of more than 70 DPJ lawmakers to win the no-confidence motion in the lower house of parliament on Thursday, a target many analysts said it was unlikely to achieve.
However, independent analyst Minoru Morita said the tide was running against the premier.
"The number of DPJ rebels is growing," he said.
NHK television said Kan's predecessor, Yukio Hatoyama, intended to vote for the motion. Hatoyama was joined by scandal-tainted party powerbroker Ichiro Ozawa, the prime minister's main rival in the DPJ.
"A strong government and a strong leader are needed in the time of a crisis," Ozawa said after the meeting of DPJ lawmakers close to him.
"I'm certain our intention will prevail in parliament."
Both Hatoyama and Ozawa head large groups of lawmakers in the DPJ.
"The question is whether Hatoyama's group will all follow him," said Sophia University professor Koichi Nakano.
Even if Kan does scrape through, analysts said it will be an uphill struggle to win support for major policies, including funding steps for an extra budget to pay for the massive rebuilding costs after the earthquake and devastating tsunami it triggered.
An Ozawa ally earlier told Reuters the rebels could have enough votes to adopt the motion, which would force Kan to resign or call a snap election.
Kan has refused to quit, saying he needs to continue his work to help resolve the crisis over radiation leakage at the earthquake-crippled Fukushima nuclear plant.
Critics within his party want Kan to quit before the no-confidence vote to clear the way for a new leader who could form a coalition with the main opposition Liberal Democratic Party (LDP) to break a legislation logjam in parliament.
"I think at the moment we have enough votes and that it's more likely that the motion will pass," Ozawa ally Kenko Matsuki told Reuters. "But we want to find a way until the very end for Mr. Kan to take the decisive step, to resign on his own, so that we can prevent that from happening."
Five Ozawa allies handed in letters of resignation from their junior cabinet posts on Wednesday to vote against Kan.
The Asahi newspaper said more than 50 backers of Ozawa, who has been charged over a funding scandal, would support the no-confidence motion.
That would be short of the more than 70 DPJ votes needed to secure passage of the motion in the 480-member lower house, where the Democrats have 305 seats, but the numbers against him could swell if large numbers of Hatoyama's group follow suit.
Also, the Japanese Communist Party and the Social Democratic Party plan to abstain from the vote, media said, lowering the number of votes needed to pass the motion against Kan.
Kan, who took office last June, is not only grappling with the crisis at Tokyo Electric Power Co's atomic plant. He must also find ways to fund rebuilding in the northeast region devastated by the tsunami and craft tax reforms to pay for rising social security costs.
The United Nation's nuclear power agency, the IAEA, criticised Japan's reaction to the crisis in a report on Wednesday, saying officials had underestimated the risks.
In a parliamentary debate with LDP leader Sadakazu Tanigaki -- off to an inauspicious start when Kan referred to his rival as "premier" -- Kan urged the opposition party to cooperate in the national crisis. Tanigaki replied that the prime minister would have to quit first.
"For the sake of rebuilding Japan, first, we must change leaders," Tanigaki said. "If you quit, we can create all sorts of new formats that supersede party lines."
The premier held out an olive branch by suggesting a parliament session set to end on June 22 could be extended -- something his critics have demanded to discuss a second extra budget to fund the next phase of rebuilding from the tsunami.
The reconstruction project will be Japan's biggest such endeavour since the years that followed World War Two.
The government also needs to get parliament to enact a bill enabling the issuance of more bonds to finance 44 percent of the $1 trillion budget for the fiscal year already begun in April.
Kan's cabinet is, in addition, trying to finalize this month proposals for social security and tax reforms -- including a likely doubling of the 5 percent sales tax in stages by 2015.
Moody's Investors Service said on Tuesday that Japan might not be able to avoid a downgrade of its sovereign debt rating even if it presented a strong reform plan, in part because of concerns over political feuding.
(Additional reporting by Kiyoshi Takenaka; Editing by John Chalmers and Sanjeev Miglani)