Since his nomination early last month, Cho, a staunch advocate of reform of the prosecution, has faced a string of allegations involving his daughter's education and his family's investment in a private equity fund, which sparked fierce partisan fighting and delayed his confirmation hearing.

One day before the hearing, fresh suspicion arose that his wife, a professor of Dongyang University, may have fabricated a school president's certificate of recognition, issued in 2012, for her daughter's voluntary work at the school's English education center. Later Cho's wife became the chief of the center.

The allegations emerged after the school's president, Choi Sung-hae, told media that he did not remember issuing such an award certificate for the daughter. 

He also said that Cho's wife called and asked him to tell the prosecution that he had entrusted her with the authority to issue the presidential certificate, stirring suspicion that she might have tried to destroy evidence. The prosecution questioned Choi on Thursday over the forgery allegation.

Later in the day, an anonymous Cheong Wa Dae official told a news outlet that a professor who recommended the certificate has been found and that relevant allegations will be clarified in the upcoming hearing.

The remark drew instant resistance from the prosecution office. 

"Today, a high-ranking official of Cheong Wa Dae suggested in a media interview that it is not a fabrication with regard to the certificate forgery allegation involving the minister nominee's wife. This can be seen as intervention in the investigation, and it is very inappropriate," the prosecution office said in a text message to reporters, citing one of its own officials.

Though the prosecution did not specify who made the remark, it is widely believed that Prosecutor-General Yoon Seok-youl was behind it.

Cheong Wa Dae immediately rebutted the prosecution's claim, saying that it has never intervened in their investigation, nor has it mentioned anything about it. The presidential office added in a message to reporters that it will watch the confirmation hearing.

It is rare for the presidential office and the prosecution to publicly clash over an investigative issue.

The prosecution has been intensifying its probe into the allegations surrounding Cho, carrying out raids on scores of locations related with his family members since last week. 

The prosecution's relatively swift investigation has raised the eyebrows of some government officials and ruling party lawmakers.

They criticized the prosecution for trying to affect the confirmation hearing.

In a parliamentary meeting on Thursday, Prime Minister Lee Nak-yon said that it is "inappropriate" for the prosecution to conduct such large-scale raids that affects "the procedures for the hearing, authority of verification and obligation of the National Assembly."

President Moon Jae-in nominated Cho as justice minister early last month, a move reflecting his commitment to reforming the prosecution to guarantee its political neutrality and grant more investigative power and authority to police.

 Meanwhile, the Korean Society of Pathologists decided late Thursday to cancel a controversial paper for which Cho's daughter was listed as the first author. 

It was published in the society's journal in 2008 after the daughter, then a high school student, took part in a two-week internship program under a medical professor who was listed as the corresponding author. 

Media and opposition lawmakers alleged she used the dubious authorship to gain admission at a prestigious college. Cho's side denied the claim. (Yonhap)