Former Japanese senior vice justice minister Mito Kakizawa, a lawmaker who belonged to the ruling Liberal Democratic Party, was arrested Thursday over allegations of vote-buying in a Tokyo ward mayoral election in April, prosecutors said.

The arrest of Kakizawa, together with four of his secretaries, is set to deal another blow to Prime Minister Fumio Kishida's administration, which has been rocked recently by a political funds scandal involving the LDP's biggest faction.

Mito Kakizawa. (Kyodo)

The 52-year-old House of Representatives lawmaker is suspected of having used around 2.6 million yen ($18,000) to support Yayoi Kimura in her successful campaign for election. The payment is judged to have been an effort to buy votes, the prosecutors said.

Kakizawa has denied the allegations, saying he offered the money to several Koto Ward assembly members as a customary mid-campaign contribution ahead of a ward assembly election also held in April, sources close to the matter said.

In November, Kimura stepped down over her use of a paid advertisement urging people to vote for her on YouTube. Her office said she paid some 140,000 yen using her credit card for the advertisement. Paid advertisements online for specific candidates, rather than political parties, are prohibited by the election law.

Kakizawa, son of former Foreign Minister Koji Kakizawa, became the first incumbent lawmaker to be arrested since Masatoshi Akimoto, who also belonged to the LDP, was apprehended in September over bribery allegations involving the wind power business.

Prosecutors apparently waited to arrest Kakizawa until after the extraordinary parliamentary session ended in mid-December. Under Japan's Constitution, lawmakers "shall be exempt from apprehension while the Diet is in session."

According to the sources, Kakizawa told his secretaries and others prior to the mayoral election to distribute 200,000 yen evenly among Koto Ward assembly members with ties to the LDP.

Kakizawa is also suspected of pressuring Kimura to use the online advertisement, which cost about 380,000 yen, in her campaign. He resigned as senior vice justice minister in October after admitting that he had proposed using the YouTube ad.

Violators of the public offices election law on vote-buying face imprisonment of up to three years or a fine of up to 500,000 yen. Those who use paid advertisements online for specific candidates face imprisonment of up to two years or a fine of up to 500,000 yen.

File photo shows staff from the Tokyo District Public Prosecutors Office carrying out items confiscated during a search the office of House of Representatives member Mito Kakizawa in Tokyo's Koto Ward on Nov. 16, 2023. (Kyodo)

In the latest development related to the scandal involving the party's largest faction, meanwhile, prosecutors searched the Tokyo office of LDP House of Councillors lawmaker Yasutada Ono.

Ono is believed to have received over 50 million yen from the faction's slush fund earned through fundraising parties over five years through 2022, the period for which the statute of limitations has not expired under the political funds control law, the sources said.

Ono is one of a number of lawmakers in the faction who are alleged to have received significant amounts of money, the sources said. The faction was formerly led by the late Prime Minister Shinzo Abe.

Following the investigation by prosecutors into the LDP member, Kishida, who heads the ruling party, told reporters he felt the necessity to "restore public trust in politics with a strong sense of crisis."

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