Questions over the sale of state-owned land at a huge discount to a school operator with ties to Abe’s wife, Akie, have dogged Abe since the matter became public last year.
Abe and his wife have denied any wrongdoing.
Aso told a news conference on Friday that several officials at his ministry’s division in charge of the sale were involved in altering the documents.
He did not say why the documents were altered.
The 77-year-old Aso apologized for his ministry’s actions but said he had no intention to resign.
“It’s extremely regrettable and I apologize for this,” Aso told reporters, when asked whether he felt responsible as head of the ministry involved in the alterations.
Abe, now in his sixth year in office, has repeatedly denied he or his wife did favors for school operator Moritomo Gakuen, which bought the land, and has said he would resign if evidence were found that they had.
Suspicions of a cover-up could slash Abe’s ratings and dash his hopes of a third term as leader of the ruling Liberal Democratic Party (LDP). Victory in the LDP September leadership vote would put him on track to become Japan’s longest-serving premier. The matter has also led to opposition calls for Aso, who doubles as deputy premier, to resign.
“The involvement of Mrs. Abe has deepened. This has entered the stage where the responsibility of the prime minister himself will be called into question,” opposition Democratic Party leader Yuichiro Tamaki, was quoted saying by Kyodo news agency.
A finance ministry official said that 14 items had been altered in the documents after February — when the scandal broke - at the instruction of the ministry’s finance division to match testimony in parliament.
Chief Cabinet Secretary Yoshihide Suga on Monday did not directly respond to a question by reporters about Akie Abe but said that the finance minister Aso should investigate the facts.
“What is important is to make everything clear,” he said.
Writing by Linda Sieg; Additional reporting by Takaya Yamaguchi, Kaori Kaneko, Yoshifumi Takemoto and Nobuhiro Kubo; Editing by Michael PerryOur Standards:The Thomson Reuters Trust Principles.