TOKYO (AFP) - Rare scandal was swirling around Japan's Prime Minister Shinzo Abe on Friday (Feb 24) as he was forced to deny involvement in a shady land deal by a religious school.

A growing controversy over the purchase of state land by a fierce nationalist at well below market rates intensified in parliament over the past week, with auditors pledging to look into the sale.

That led Abe on Friday to pledge he would resign if any wrongdoing was uncovered.

"I will take responsibility as a politician if my wife and I were involved," he said.

The issue centres on the purchase last year of a plot of land in Osaka by the right-wing operator of an ultra-conservative kindergarten.

Media say the school, Moritomo Gakuen, paid just 134 million yen (S$1.68m) for the 9,000 square metre plot - around a tenth of the cost of a nearby plot of a comparable size.

Until recently, the kindergarten's website said Abe's wife, Akie, would become honorary principal at the new primary school it was building on the land.

The suggestion among his opponents was that the operator Yasunori Kagoike had only got such a good deal on the land because of his connections to the prime minister.

Abe, pressed in parliament on Friday, acknowledged that his wife Akie had once "reluctantly" accepted the post of honorary principal, but had since "resigned".

The prime minister also said that he complained to Kagoike, who had attempted to use his name to help raise money for the school, which is due to open in April.

Kagoike had collected donations by saying the new institution would be named the "Shinzo Abe Memorial Primary School," Abe said.

"It was before I became prime minister and I declined it at that time," he said.

The left-leaning Tokyo Shimbun on Friday said the issue was "grave".

"Parliament should throroughly investigate and clear up the suspicions," it said in an editorial.

Abe's more than four years in the job have been unblemished by the kind of grubby money scandals that regularly claim scalps in Japanese politics.

It is unclear how much impact the present controversy will have on a prime minister who still enjoys high approval ratings.

But the case has underscored the strong support Abe has among far right-leaning businessmen, politicians and media.