Japanese Prime Minister Fumio Kishida was grilled in parliament on Tuesday over allegations that his and four other major factions of the ruling Liberal Democratic Party have underreported their incomes from fundraising parties.

In an extraordinary Diet session, Kishida explained that he became aware of the issue only when officials briefed him that his intraparty group corrected its funds reports, exacerbating the challenges his Cabinet faces amid sluggish support rates.

Japan's law obliges political groups to list the names of organizations and individuals that purchase party tickets worth more than 200,000 yen ($1,350) in their funds reports.

Japanese Prime Minister Fumio Kishida (C) heads to a House of Representatives Budget Committee session in Tokyo on Nov. 21, 2023. (Kyodo)

Prosecutors have started questioning officials of the factions on a voluntary basis as the five groups are alleged to have underestimated their party revenues by around 40 million yen between 2018 and 2021, sources close to the matter said.

Hiroshi Kamiwaki, a constitutional professor at Kobe Gakuin University, has looked into the allegations and submitted a criminal complaint over the case with prosecutors.

"As such a thing should not happen again, we will appropriately deal with it," Kishida said in responding to a question by Kenta Izumi, chief of the leading opposition Constitutional Democratic Party of Japan.

By group, the largest faction formerly led by slain Prime Minister Shinzo Abe allegedly underreported about 19 million yen, followed by former Secretary General Toshihiro Nikai's group at some 9.5 million yen and Secretary General Toshimitsu Motegi's team at around 6 million yen, according to Kamiwaki.

The intraparty group led by former Prime Minister Taro Aso appears to have underestimated about 4 million yen, with the fourth-largest faction headed by Kishida seemingly lessening its party revenues by some 2 million yen in its funds reports.

Among LDP members, former House of Representatives lawmaker Kentaro Sonoura was convicted of underreporting some 49 million yen collected from several fundraising parties in December 2022.

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