Tokyo: Japanese Prime Minister Shinzo Abe said on Monday that although the man at the centre of a scandal about approval for a school was an old friend, he had "never once" tried to use that relationship to gain favours.

Abe and his aides have repeatedly denied intervening to help Kake Gakuen (Kake Educational Institution) win approval for a veterinary school in a special economic zone. Its director, Kotaro Kake, is a friend of Abe.

Abe faces a grilling in parliament on Monday over a suspected scandal that has cut his ratings to their lowest since taking office in 2012 and after a candidate from his ruling party lost a mayoral election. 

Also appearing at the ad hoc committee session will be his aide, Hiroto Izumi, and Kihei Maekawa, who resigned as the education ministry's top bureaucrat in January and has accused the government of distorting the approval process.

The scandals, and a perception among many voters that Abe's administration is taking them for granted, are encouraging rivals and casting doubt on Abe's hopes for a third term as ruling Liberal Democratic Party leader.

Several opinion polls have shown Abe's support below 30 per cent and, while this does not immediately threaten his job, it does cloud the longer-term outlook. 

A July 22-23 Mainichi newspaper poll published on Sunday showed Abe's support slipping 10 points to 26 per cent from the previous survey in June. It also showed that 56 per cent of respondents did not back Abe's government, a 12 point rise.

Abe was until recently seen as being on track to become Japan's longest-serving prime minister by winning a third three-year term when his current tenure ends in September 2018.

Further pressure is likely to come from Sunday's victory by an opposition candidate in the mayoral election for the northern city of Sendai. Abe's party suffered a devastating defeat in elections for the Tokyo assembly earlier this month.

Earlier this year, the head of a Japanese nationalist school testified under oath in parliament that he received a donation of 1 million yen ($11,700) from Abe's wife in her husband's name and resigned as honorary principal of a new elementary school planned by a right-wing group in Osaka.

The group, Moritomo Gakuen, bought land from the government at a fraction of its appraisal price to build an elementary school. Abe denies any wrongdoing.

Abe is expected to reshuffle his cabinet early next month in an effort to repair his damaged ratings, a step that can backfire if novice ministers become embroiled in scandals or make gaffes.

Also in trouble is Defence Minister Tomomi Inada, an Abe protege, who faces calls to resign over media reports of direct involvement in a ministry cover-up of documents about a sensitive peacekeeping operation. She denies the reports

Opposition lawmakers are also expected to grill Abe about media reports that Inada allowed defence officials to conceal logs about the activities of the Self-Defence Forces, as Japan's military is known, in a UN-led peacekeeping operation in South Sudan.

Reuters