Japanese prosecutors have asked former Prime Minister Shinzo Abe to explain allegations that his political group illegally covered shortfalls in the cost of dinners for supporters, sources close to the matter said Thursday.

The prosecutors have also decided to build a case against one of his state-paid secretaries for allegedly not recording incomes and expenditures related to the dinner functions. The total income and costs not declared in political fund reports possibly exceed 40 million yen ($383,000), they said.

The prosecutors plan to question Abe sometime after the current extraordinary Diet session ends Saturday. The former premier, however, told reporters at parliament he had no knowledge of such a request.

Photo taken in April 2019 shows Japanese Prime Minister Shinzo Abe addressing a cherry blossom viewing party in Shinjuku Gyoen National Garden in Tokyo. (Kyodo) ==Kyodo

Abe is expected to be questioned about whether he was aware of his secretary's failure to record the incomes and expenditures related to the dinner functions.

The latest development could weaken Abe's political clout and deal a blow to his successor Yoshihide Suga, who served as chief Cabinet secretary under Abe and defended the then leader over the scandal during press conferences and parliamentary sessions.

Abe, who became the country's longest-serving prime minister before stepping down in September due to health reasons, has repeatedly denied any wrongdoing after the scandal came to light in November last year.

People close to Abe have said the secretary offered false explanations when quizzed by the former premier over the matter.

The secretary heads a group of Abe's supporters that hosted the dinner functions between 2013 and 2019 on the eve of the government-sponsored annual cherry blossom-viewing parties, according to the sources.

The total bills for the events held at two luxury hotels in Tokyo reached 23 million yen over a five-year period through last year, far higher than the amounts collected from attendees, many of whom were voters in Abe's constituency in Yamaguchi Prefecture, western Japan.

According to the sources, the party attendees paid only 5,000 yen each, even though such events at the five-star hotels normally cost about 11,000 yen or more per head.

To make up for the shortfalls, Abe's side paid more than 1 million yen every year, with the largest amount reaching around 2.5 million yen, the sources said.

The secretary has confirmed Abe's side made up for the shortfalls during voluntary questioning, they said.

In response to media reports that his aide had been questioned by the prosecutors, Abe told reporters last week that his office is "fully cooperating with the investigation. I can't say anything more than that at this stage."

The prosecutors believe a fund management organization led by Abe covered the shortfalls because the hotels issued receipts addressed to it.

Neither the supporters' group nor the fund management body recorded their incomes and expenditures linked to the functions between 2015 and 2019 in their political fund reports. There is also a suspicion that the receipts have been discarded, according to the sources.

Opposition parties ramped up criticism of the government on Thursday, demanding the former prime minister be summoned to parliament to offer explanations over the matter.

Referring to Abe's past denials in parliament of any wrongdoing, Jun Azumi, the Diet affairs chief of the major opposition Constitutional Democratic Party of Japan, told reporters, "(Abe) should explain about the lies he told in the Diet in the same place that he told them."

Related coverage:

2 key Shinzo Abe staff may have led decision to illegally cover dinner cost

Abe's office may have disposed of receipts for hotel functions