Abe, who resigned in August, apparently due to ill health, volunteered for questioning this week as prosecutors sought to build a case against his secretary over unreported political funds.
He is under pressure to address allegations that a local association of political supporters – known as a support group in Japan – helped cover dining expenses for his constituents to attend the government’s annual cherry blossom viewing parties in Tokyo between 2015 and last year.
The failure to list the expenditure in annual fund reports is a possible violation of political funding laws.
The constituents, who travelled to Tokyo from Abe’s constituency in Yamaguchi prefecture, western Japan, paid just ¥5,000 (£36) each to have dinner at expensive hotels on the eve of the cheery blossom events, according to the Asahi Shimbun.
Hotel receipts showed that the full cost of the banquet-style meals at two luxury hotels came to a total of ¥23m over five years. Abe’s secretary confirmed to prosecutors that the support group had made up the shortfalls.
Abe’s support group, led by his taxpayer-funded secretary, is suspected of contributing ¥9.16m over the period, the Asahi said.
As prime minister, Abe repeatedly told MPs there had been no impropriety. Kyodo news agency reported late on Tuesday local time that prosecutors were not planning on taking action against him.
Hosted by prime ministers almost every year since 1952, the cherry blossom viewing party is a springtime event originally meant to honour sportspeople, celebrities and other citizens who have excelled in their fields, but critics say it is increasingly used to reward the government’s political supporters.
The scandal risks tarnishing Abe’s legacy and could weaken Suga, who was his preferred successor when he stepped down saying he required treatment for a recurrence of a chronic bowel condition.
Suga, who was Abe’s chief spokesman for almost eight years, publicly defended the then prime minister when the allegations were first reported last year.
Pressure is building on Abe to give unsworn testimony before a parliamentary budget committee, possibly before the end of the year.
Opposition MPs have demanded he explain where the money for the dinner parties came from and why he had previously denied payments were made to help cover the costs.
Abe said last week he was willing to address the allegations in parliament. “I will deal with [any questions] sincerely after prosecutors finish their investigation,” he told reporters.
Demands for a parliamentary appearance have come from supporters of his own party. According to a Kyodo news agency poll, 53% of LDP voters said he should testify, against 43% who thought it was unnecessary.
The investigation has come at an awkward time for Suga, who faces an LDP presidential race next September and a lower house election the following month.
His approval ratings have plummeted over his handling of the coronavirus pandemic, with many voters criticising his decision to wait until last week to suspend a subsidised travel scheme that experts say may have helped the virus spread since it was launched in July.
Support for his cabinet fell to 39% from 56% a month earlier, a weekend poll in the Asahi showed, with 79% of respondents saying his decision to pause the “Go To Travel” campaign came too late.
Suga has also drawn criticism for attending dinners despite asking the public to avoid eating and drinking in groups of more than four during the year-end party season.
On Monday, he said he saw no need to declare a state of emergency in an attempt to contain the latest outbreak, despite warnings that hospitals are struggling to cope with the influx of Covid-19 patients. Abe called a state of emergency in April in response to the first wave of infections.
Suga said the head of the government’s expert panel on the pandemic had told him “we’re not there yet” with regards to declaring a state of emergency.
While Japan has fared better than many other countries during the pandemic – with just over 200,000 cases and 2,978 deaths – a record 2,154 people were being treated in hospital for the virus as of Monday, NHK said.