Koichi Kato, who has stirred up a power struggle within the ruling Liberal Democratic Party, said he will do "everything possible" short of quitting the party to bring about the downfall of Prime Minister Yoshiro Mori.
Kato, a former LDP secretary general who covets the prime ministership, said in an interview with Kyodo News that he will base his actions "on the assumption that I will not leave the LDP." However, he said he will not rule out abstaining or voting in favor of a no-confidence motion the opposition parties plan to submit to the Diet.
Such options "are in sight," said Kato, who heads the LDP's second-largest faction.
Kato, a reformer long viewed as one of the top candidates to succeed Mori, has put pressure on the prime minister to step down by threatening to abstain from or even support the no-confidence motion. Taku Yamasaki, who heads another LDP faction, has said he will follow Kato.
If a no-confidence motion is approved, the Mori Cabinet would have to resign or dissolve the House of Representatives and call a general election.
Kato said his actions are "not merely a short-story drama."
"Just changing the front cover wouldn't work," he said. "My moves represent a great venture to create brand-new politics. I'm confident of ultimate victory."
Asked about the chances of forming his own Cabinet, Kato declined comment, but said, "We should not discuss the third and fourth acts when act one of a drama is still in progress."
Four opposition parties -- the Democratic Party of Japan, the Liberal Party, the Japanese Communist Party and the Social Democratic Party -- jointly hold 190 of the 480 seats in the powerful Lower House. The ruling camp holds 272.
Of that number, the Kato faction holds 45 seats and the Yamasaki faction 19.