Former Japanese Justice Minister Katsuyuki Kawai and his lawmaker wife Anri were arrested Thursday for allegedly giving millions of yen in cash to local politicians as rewards for their efforts to secure votes for her in last year's upper house election, prosecutors said.

The arrests may deal a further blow to Prime Minister Shinzo Abe given his ties to Kawai, who served as his special adviser for foreign affairs and then briefly assumed the post of justice minister after the election last July.

It is the first time in 18 years that a Japanese lawmaker who was a Cabinet member has been arrested by Tokyo prosecutors. The Abe administration has already seen its support rate take a hit over the prime minister's handling of the coronavirus pandemic and a gambling incident involving a former top prosecutor.

The 57-year-old Kawai, a lower house member, allegedly offered a total of 1.7 million yen ($16,000) to five people in collusion with his wife prior to the election, and around 24 million yen by himself to 91 people from around late March to early August last year, in return for mobilizing support for her during the campaign, according to the prosecutors.

Most of the people who were questioned by the prosecutors, including prefectural and city assembly members, heads of local governments as well as supporters in Hiroshima Prefecture, have admitted to receiving cash, according to investigative sources.

One of the sources said the maximum amount paid per person was more than 1 million yen.

The 46-year-old Anri Kawai won her first parliamentary seat in the House of Councillors election, after gaining strong support from the premier's office and the headquarters of Abe's Liberal Democratic Party.

During several rounds of voluntary questioning, the couple denied the vote-buying allegations against them, the sources said.

On Wednesday, Abe's LDP accepted the resignation of the couple. However, they told the party they intend to continue serving as parliamentarians.

In response to the arrests, opposition parties criticized Abe for having appointed Kawai as the minister and called for intensive parliamentary discussions.

Yukio Edano, leader of the main opposition Constitutional Democratic Party of Japan, urged Abe to step down, saying, "The prime minister's discretion is questionable as he appointed as justice minister a person whose behavior could lead to his arrest."

The arrests came after parliament ended a 150-day ordinary session that ran through Wednesday. Lawmakers have special immunity from arrest while the Diet is in session.

Abe offered an apology over the arrests. "I'm keenly aware of my responsibility," he said at the outset of a nationally televised press conference to mark the end of the Diet session.

The prosecutors have found that the former justice minister orchestrated the campaign on behalf of his wife.

After the Kawais were arrested, the Tokyo District Public Prosecutors Office's special investigative team searched various places linked to them, including their political offices and their rooms in a condo complex for Diet members in Tokyo.

In the upper house election, Anri Kawai, a former prefectural assembly member, was running to win one of the two seats available in the Hiroshima constituency but faced concerns she would split the vote with a fellow LDP candidate, the then-incumbent veteran Kensei Mizote.

Mizote failed to win re-election due to the conservative vote being split, with another incumbent backed by opposition parties retaining the seat.

The LDP headquarters offered an unusually large amount of 150 million yen to Kawai's camp during the campaign and the prosecutors are examining whether the cash was drawn from the fund and given to supporters prior to the election.

The money provided to Mizote's camp was 15 million yen, which is considered the average amount to be given by the LDP for an election campaign, according to a person familiar with the matter.

Speaking to reporters on Wednesday, Kawai offered an apology for causing trouble to all parties concerned.

However, he maintained his political activities have never been in breach of the law.

His wife declined to comment on the advice of her lawyer.

Abe appointed Kawai, a seventh-term House of Representatives member, as justice minister, his first ministerial post, in a Cabinet reshuffle in September. However, he stepped down the following month in the wake of a separate money scandal over his wife's election campaign.

On Tuesday, Anri Kawai's state-paid secretary was sentenced to 18 months in prison, suspended for five years, for illegally paying campaigners during the upper house election.

She will lose her seat when the secretary's sentence is finalized, allowing a court to recognize the prosecutors' request for the application of guilt by association to the election law.