NHK has learned that Tokyo prosecutors are considering building a case against a former chief treasurer of a ruling party faction previously led by Prime Minister Kishida Fumio over suspected political fund irregularities.

The prosecutors have been looking into a scandal embroiling factions of the main ruling Liberal Democratic Party over off-the-book revenues from fundraising parties. The largest intra-party faction that was once led by the late Prime Minister Abe Shinzo is among those under scrutiny.

Sources familiar with the matter say the ex-treasurer is suspected of failing to report about 30 million yen, or 200,000 dollars, as revenues from the Kishida faction's fundraising parties over three years to 2020.

The former treasurer is suspected of falsifying political funding reports in violation of the political funds control law.

The sources say the person admitted to not declaring part of the revenues from fundraisers when questioned by prosecutors on a voluntary basis.

Kishida had led the faction since 2012, but left the group last December as the money scandal widened. He said he would try to restore people's trust in politics from a more neutral position.

The prime minister told reporters on Thursday that there were clerical mistakes in the faction's fund reports. He said the faction would file corrections with the internal affairs ministry.

The revised reports for the three years to 2022 show that the faction failed to report nearly 9 million yen, or about 60,000 dollars, in 2020 alone.

Tokyo prosecutors are also apparently preparing to indict, without arrests, chief treasurers of the Abe faction and the faction led by former LDP Secretary-General Nikai Toshihiro.

The Abe faction is suspected of failing to report revenues from fundraisers totaling over 600 million yen, or 4 million dollars, over five years to 2022. Similarly, the Nikai faction allegedly kept over 200 million yen, or 1.35 million dollars, off the books.

Tokyo prosecutors are also setting their eyes on Nikai's office. Sources say they are considering building a case against one of Nikai's secretaries on suspicion of violating the political funds control law.

The prosecutors say Nikai's office is suspected of not handing over more than 30 million yen in revenues from fundraising parties to the faction and keeping the money in its own coffers, without reporting it.

Sources say that during questioning on a voluntary basis, the secretary admitted to keeping part of the revenues from parties and not recording it in the office's funds reports.