The nation's police chief pledged Monday to investigate claims that high-ranking police officers had tried to affect the outcome of a police probe into allegations that government spy agents intervened in December's presidential election.

Wrapping up a four-month-long probe, Seoul's Suseo Police Station announced Thursday that two National Intelligence Service agents had illegally intervened in politics by posting a slew of politically sensitive comments on the Internet ahead of the Dec. 19 presidential vote.

A day later, Kwon Eun-hee, a police officer who led the investigation into the scandal, claimed that high-ranking national police officers had tampered with the police probe.

"Regardless of the backdrop of the disclosure, we, if necessary, will conduct a fact-finding probe into what has been claimed," Lee Sung-han, head of the National Police Agency, told reporters.

Police auditors will look into Kwon's claim, he said, adding that the police officer could also be subject to an inspection if her claims are found to be wrong or inflated.

The Seoul Central District Prosecutors' Office also launched a special investigation team to look into the case. The main opposition Democratic United Party is demanding a thorough probe, claiming that the earlier police investigation had been doctored.

As an example of undue influence from her superiors, Kwon cited that her team initially had asked the Seoul Metropolitan Police Agency to analyze all computer files that included 78 key words but the agency later cut down the number to four.

On Monday, SMPA officials refuted Kwon's claim, arguing that they had never unilaterally asked her to reduce the number.

"Because it takes considerable time to analyze documents with one key word, we decided to remove some key words that had no direct relevance to the investigation," an SMPA official said, requesting that he not be named.

Kim Jung-sug, chief of the SMPA, refused to elaborate on the cover-up allegation.

"It's improper for me to say if the allegation is wrong or not," Kim said. "The ongoing probe by prosecutors will ultimately unveil full truth about the case.

Also on Monday, the Seoul prosecution office said its special probe team will take over a similar complaint being separately probed by a criminal investigative department.

Later in the day, Kwon said she was just doing her job when she made such allegations.

"(I) know that I can be the subject of the inspection," Kwon said in an interview with Yonhap News Agency, adding that she, as a responsible person who led the investigation at the time, was obliged to tell the truth.

She also disclosed that she had received a phone call from one of her superiors not to disclose to the press any details regarding the probe.

"A high-ranking official called me when a female NIS agent was being summoned for questioning and warned that he will get me if I say a word to the (press,)" Kwon said.

She also said she feels uncomfortable being called by the media a "whistle-blower" or "hero."

Meanwhile, amid mounting public criticism into police initial probe, Justice Minister Hwang Kyo-ahn vowed he will order a thorough investigation into the scandal, saying that the prosecution probe will be conducted in accordance with the law and the principle.

"I will guide the prosecution so that the people will not have any doubt" Hwang said during a meeting with lawmakers at the National Assembly. (Yonhap News)