TOKYO, March 27 (Xinhua) -- A key figure in a document-tampering scandal involving Japan's Finance Ministry appeared in the Diet on Tuesday to give sworn testimony over the falsification of government documents related to the heavily discounted sale of state land to a nationalist school operator.

Former national tax agency head Nobuhisa Sagawa, who was previously in charge of taking care of the land sale, stepped down to take account for the confusion he had caused and was under fire for potentially lying in parliament while serving as director general of the ministry's Financial Bureau.

He appeared as a sworn witness at the House of Councillors' Budget Committee Tuesday morning and will attend another session in the House of Representatives' panel in the afternoon.

The Finance Ministry has conceded that 14 documents related to the cut-price land transaction were altered between late February and April last year after officials at the Financial Bureau ordered its regional bureau in Osaka to do so and insisted Sagawa play a key role.

Sagawa initially denied in parliament any instances of influence-peddling regarding the land sale and stated that there had been previous negotiations with Moritomo Gakuen over the land price prior to its sale.

He also said the ministry had ignored the records of the negotiation.

But it was later found that references to Prime Minister Shinzo Abe, his wife Akie and other senior ministers, along with the negotiation records were included in the original documents.

Akie Abe was set to become honorary principle at the elementary school to be built on the state land sold to the school operator for just 14 percent of its appraisal value.

The documents were thereafter altered to presumably remove the names of the prime minister and his wife and other senior lawmakers from being disclosed in the Diet last year.

The Finance Ministry said the documents were altered so that they would be in line with Sagawa's testimony when he was quizzed in the Diet.

Sagawa had been under pressure from opposition parties for allegedly making false parliamentary remarks while serving as director general of the ministry's Financial Bureau.

According to the opposition bloc, the documents were also altered after Abe said in February last year that he would resign as prime minister if either he or his wife were proven to have been complicit in the cronyism scandal.

The opposition camp are gearing up to summon Akie Abe and others to give soon testimony in a bid to conclude the protracted scandal, according to recent media polls.