TOKYO (Reuters) - Tokyo Governor Yuriko Koike, whose new political party poses a growing threat in elections later this month, denied speculation that she would run, the Yomiuri newspaper reported on Tuesday (Sept 3).

Koike's fledgling Party of Hope has emerged as a growing challenger to the bloc led by Prime Minister Shinzo Abe's Liberal Democratic Party (LDP) since Abe called the snap Oct 22 poll last month.

"I have been saying I will not run for the election from the beginning," Koike said in an interview with the Yomiuri.

"I'm 100 per cent not running for the election", it quoted her as saying in her strongest denial to date.

Abe called the poll in the hope his bloc would keep its two-thirds "super majority" in the lower house.

Koike must decide whether to run for a seat in parliament to become eligible for the top job, or wait and bet her party positions itself to win the next national poll.

On Monday, she told Jiji news agency her party aimed to run more than the 233 candidates needed to take a majority in the 465-seat lower house.

"If you don't buy a lottery ticket, you can't win," she said.

Koike, a media-savvy former LDP member and defence minister, has said she would not resign as governor to run now, especially ahead of the 2020 Tokyo Olympic Games.

But the 65-year-old has made no secret of her desire to be Japan's first female prime minister - she even named her pet terrier "Sori", Japanese for "premier".

There has been speculation that she will run, perhaps announcing on Thursday (Oct 5), when the Tokyo Metropolitan assembly ends its session. Candidates must register on Oct 10, when the campaign officially starts.

If Koike resigns as governor little more than a year after defying Abe's LDP to run successfully for that post, she would risk a backlash from voters.

Waiting might let her best shot at the premiership slip through her fingers.

"If she thinks of the nation, it is important that she boldly announce her candidacy, present her ideas about important matters ... and debate policies head on," Abe's ally, Chief Cabinet Secretary Yoshihide Suga, told reporters on Monday.

Koike's close ally, Masaru Wakasa, on Sunday said it was not essential that she run this time around. "If there is a firm prospect of a change in government, party chief Koike might run for parliament, but if we can achieve a change in the 'next, next' election, she doesn't have to run now," Wakasa said during a debate on NHK.

A TV Asahi survey published on Monday showed 72 per cent were negative about her potential candidacy. A separate NHK poll showed voters were split on Koike's new party, with about 47 per cent having hopes for it versus the same percentage who had little or no expectations.

Koike's cool, polished demeanour belies a steeliness beneath.

"She can take a punch with a smile and sharpen her knives at the same time," said Jesper Koll, head of equity fund Wisdom Tree, who has followed Japanese politics for years.

Like former prime minister Junichiro Koizumi, one of her past mentors, Koike promises to "break free of vested interests", a slogan that resonates with voters looking for an alternative to the LDP - although critics question just how different that alternative would be from Abe's LDP.

To differentiate her party from the LDP, Koike has adopted popular policies, such as an end to atomic power amid public safety worries after the 2011 Fukushima nuclear crisis, and proposes to freeze a planned sales tax hike from 2019.

But she also backs Abe's push to expand the role of the military overseas and his goal of revising the post-war Constitution - although recently she has avoided focusing on the divisive issue of amending its pacifist Article 9.

She has also said in the past that Japan should consider having nuclear weapons, breaking a taboo in the only country to suffer an atomic attack, and, like Abe, has visited Yasukuni Shrine for war dead, seen in China and South Korea as a symbol of Japan's past militarism.