TOKYO (Reuters) - Popular Tokyo Governor Yuriko Koike, whose fledgling conservative party poses a growing challenge to Prime Minister Shinzo Abe’s ruling bloc, agreed on Saturday to cooperate in next month’s election with a small party based in western Japan.

Tokyo Governor Yuriko Koike, head of Japan's Party of Hope, attends a news conference at the Japan National Press Club in Tokyo, Japan September 28, 2017. REUTERS/Kim Kyung-Hoon

The deal potentially broadens the geographic reach of Koike’s new Party of Hope, formally launched just this week, ahead of the Oct. 22 poll.

Abe called the election hoping to keep his conservative Liberal Democratic Party-led coalition’s majority in parliament’s lower house, where it had a two-thirds “super” majority before dissolution.

But Koike has upended the political landscape with her new party and some Japanese believe she could become the country’s first female premier.

Koike and Osaka Governor Ichiro Matsui, who heads the small conservative Japan Innovation Party, announced the deal to coordinate candidates in Tokyo and Osaka, western Japan, at a news conference with Hideaki Omura, governor of Aichi prefecture in central Japan and the head of a tiny local party.

“In a situation where ‘Abenomics’ is stalled, we must proceed with reform in each region,” Koike told the joint news conference in Osaka, referring to Abe’s economic policies.

“We have agreed to mutually cooperate in the coming election with those who share that aspiration,” she added.

Koike’s Party of Hope is already cannibalizing the failed main opposition Democratic Party, which in a stunning move this week decided to have its lower house members leave the party and run on her ticket. The party, a mix of conservatives and liberals, had struggled with rock-bottom support and defections.

Koike, a former LDP lawmaker and defense minister, has said she would only take in those who agree with her conservative stance on security policies, leaving liberals out in the cold.

Abe, for his part, is warning that Koike’s new party would cause bring “confusion, not hope” and stressing that the LDP-led coalition is the only reliable choice at a time of rising tensions over North Korea’s missile and nuclear arms programs.

“North Korea has twice launched missiles over Japan,” he said in remarks carried by NHK public broadcaster. “We must join with international society to meet this threat.”

Last year, Koike infuriated the LDP’s Tokyo branch by running for governor without party approval. She defeated her LDP rival by a landslide and then led a novice local party to a historic win with the backing of Abe’s junior coalition partner.