Abe's government has faced mounting pressure in recent days over the 2016 sale of state-owned land to one of his supporters at a price well below market value.

"Changing official documents is very grave and extremely regrettable and I deeply apologise," Finance Minister Taro Aso said at a hastily convened press conference.

"What is important is that these things don't happen again," Aso added. "We are fully cooperating with the investigation."

The scandal first emerged early last year, but resurfaced after the revelation that official documents related to the sale had been altered.

Aso blamed the changes on "some staff members" at the ministry, and said he had only learned about them on Sunday.

And he dismissed suggestions that he might resign over the scandal.

"I am not thinking about that at all," he said.

He said 14 changes had been made to the documents but said he did not believe the alterations were intended to protect Abe and his wife.

'Debased democracy'

Versions of the original and the doctored documents published Monday by opposition lawmakers appeared to show Abe's name had been scrubbed, along with that of his wife Akie, and Aso.

"What became clear is that they debased democracy," by lying to parliament, said opposition lawmaker Renho, who uses one name.

Opposition politicians have alleged that the buyer of the land -- a right-wing operator of private schools -- was able to clinch the sale at such a favourable price because of his ties to the Abe family.

The operator had named Akie Abe the honorary principal of the school he was planning to build on the government plot.

Aso said the documents were doctored to be "coherent" with a speech made in parliament by the head of the tax agency Nobuhisa Sagawa, who stepped down on Friday over the scandal.

Sagawa was head of the finance ministry department that oversaw the land deal, before being promoted last year to tax agency chief.

"It is possible that Sagawa ordered the alterations," the Mainichi Shimbun newspaper said, citing government sources.

Adding to the pressure, a finance ministry official linked to the scandal was found dead on Friday, although it is not clear if the reported suicide is linked to the affair.

Abe has consistently denied any wrongdoing and vowed to resign if he was found to be involved in the land deal.

But a poll released published Monday in the Yomiuri Shimbun showed his support dropping by six percentage points from last month to 48 percent, the first reading under 50 percent since he won re-election in October.

Eight out of 10 voters said the government was not responding appropriately to the allegations, according to the survey conducted over the weekend among 1,036 voters.

The allegations have also paralysed parliament in recent days, with some opposition lawmakers boycotting debates.

AFP

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