TOKYO — Japan's incoming Prime Minister Shigeru Ishiba said Monday he plans to call a general election on Oct 27 as he prepares to take office.

The lower house of the parliament will be dissolved on Oct 9, Ishiba told reporters, emphasizing the importance of obtaining the public's mandate as soon as possible.

The 67-year-old former defense minister narrowly defeated Economic Security Minister Sanae Takaichi in a run-off on Friday to lead the country's ruling Liberal Democratic Party (LDP).

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As the LDP-led coalition constitutes a majority in both chambers of the parliament in Japan, Ishiba, as the new party chief, is set to be elected prime minister in an extraordinary Diet session on Tuesday to succeed Fumio Kishida.

In Japan, a new prime minister often calls a snap election to dissolve the lower house at an early date to capitalize on a high approval rating to seek a public mandate and pursue his political agenda.

At a press conference following his win on Friday, Ishiba has vowed to give his "full effort" to rebuild trust and unity within the LDP, calling for a party that is humble, fair, and transparent, where rules are followed, and the public can hold leaders accountable.

Japanese shares fell more than 4 percent in early trading on Monday as the yen strengthened and Japanese government bonds jumped in reaction to the leadership win by Ishiba, who is seen as a monetary policy hawk.

Ishiba on Monday began picking government and party officials who will contest the upcoming general election with him.

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So far those include two rival candidates in the leadership race, Katsunobu Kato as finance minister and Yoshimasa Hayashi to stay on as chief cabinet secretary, a pivotal post that includes the role of top government spokesman, two sources familiar with the appointments earlier told Reuters.

A close Ishiba ally, Takeshi Iwaya, a former defence chief, will take over as foreign minister, while Gen Nakatani will return to the defence ministry, a position he held in 2016, said the sources, who asked not to be identified because they are not authorized to speak to the media, confirming earlier media reports.

Yoji Muto, a former junior minister, will take charge at the economy, trade and industry ministry, a separate source said.

Not included in his picks, however, is Sanae Takaichi, the hardline conservative he beat by 215 votes to 194 on Friday in the closest leadership election in almost seven decades.

Takaichi's absence could make it difficult for Ishiba to manage a fractious ruling group roiled by scandals that have sapped its public support.

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Media reports that Takaichi has declined a post "could point to a weakness in Ishiba's support base, which could cause him problems going forward," said Hiroshi Shiratori, a political science professor at Hosei University in Tokyo.

Ishiba picked another rival, Shinjiro Koizumi, as his election campaign chief, along with former Prime Minister Yoshihide Suga, a Koizumi backer, who is the party's new vice-president. Both joined him at his press conference on Monday.

Ishiba, 67, won the LDP leadership race on his fifth attempt with strong backing from rank-and-file members.