Factbox-Who could replace Japan's Ishiba as leader of the ruling party?

Japanese Prime Minister Shigeru Ishiba denied talk on Wednesday that he had decided to quit after a source and media reports said he plans to step down following a bruising upper house election defeat.

Some in his own party are questioning his leadership and the opposition is weighing a no-confidence motion.

Ishiba's resignation as prime minister would trigger a leadership race in his Liberal Democratic Party (LDP), with the winner facing a parliament vote to become prime minister of the world's fourth-largest economy.

Here are the LDP lawmakers who might throw their hats in the ring:

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SANAE TAKAICHI, 64:

A Yomiuri newspaper poll following Sunday's election showed Takaichi as the top pick for prime minister in an LDP-led government, with 26% of votes, followed by farm minister Shinjiro Koizumi, at 22%.

Representing the party's right wing, she lost to Ishiba in the September leadership race in a run-off vote. Takaichi previously served as Japan's economic security minister, internal affairs minister and the LDP's policy council chief.

She is known for her conservative views, such as revising the pacifist constitution, and is a regular visitor to the Yasukuni war shrine, viewed by some Asian neighbours as a symbol of past militarism.

She also opposes allowing women to retain their maiden names, saying it would undermine tradition.

Takaichi courted controversy in 2016 when she suggested the government could revoke broadcasting licences of media companies deemed to be politically biased.

SHINJIRO KOIZUMI, 44:

The son of a former prime minister and heir to a political dynasty with a hand in governing Japan for more than a century, he would become its youngest prime minister in eight decades if he succeeded Ishiba.

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Koizumi also ran in the last party leadership race, presenting himself as a reformer able to restore public trust in a party mired in scandal.

Unlike Takaichi, who left government after her defeat in that contest, the Columbia University-educated Koizumi stayed close to Ishiba as his agriculture minister, overseeing the release of rice stockpiles in a bid to curb soaring prices of the staple.

TOSHIMITSU MOTEGI, 69:

A former foreign minister, Motegi has a reputation as a tough negotiator and handled talks with U.S. Trade Representative Robert Lighthizer when President Donald Trump was last in office.

He has also served as trade minister, economy minister and the party's secretary general.

He studied at the Harvard Kennedy School and worked at the Yomiuri newspaper and consulting firm McKinsey before entering politics in 1993.

Other potential candidates include Chief Cabinet Secretary Yoshimasa Hayashi, 64, and Finance Minister Katsunobu Kato, 69.