Prosecutors raided the National Intelligence Service on Monday as part of their investigation into alleged evidence fabrication in an espionage case.

The move came hours after President Park Geun-hye called for a thorough investigation and opposition leaders called for an independent probe and dismissal of the spy chief.

At Monday’s meeting with senior presidential staff, Park said that she considered evidence forgery as “very regretful.”

“In order to reveal the truth, the prosecutors’ investigation should leave no suspicions and the National Intelligence Service must fully cooperate with the investigation,” Park said. 

“(Any problems uncovered) must be set right.”

The case, which began last year, revolves around Yoo Woo-seong, a former Seoul Metropolitan Government official accused of spying for North Korea.

Yoo, a North Korean of Chinese descent who came to the South in 2004, was initially acquitted. But the prosecution appealed with new Chinese documents allegedly proving that Yoo had traveled to North Korea as late as 2006.

According to the prosecution, the documents were provided by the NIS, which secured them through one of its agents working at the South Korean mission in Shenyang, China.

The authenticity of the evidence, however, came into question when the Chinese Embassy in Seoul said that they were not genuine Chinese government documents.

In addition, a Korean-Chinese NIS collaborator has claimed that he forged the documents. The collaborator, identified as Kim, attempted suicide last week leaving a note saying that the NIS owed him money for the forged documents.

Since Friday, the prosecutors’ office has been operating an investigation team into the developments.

The team is set to file for an arrest warrant on Kim, and has issued travel bans on a number of NIS agents involved in the case. The prosecution is reportedly planning to summon the NIS agents in the near future for questioning.

On Sunday, the NIS issued a statement apologizing for the developments and promising to cooperate with the investigation.

The spy agency also said that agents proven to have participated in illegal activities in relation to the case will be subjected to “stern punishment.”

While welcoming the president’s statement, the main opposition Democratic Party did not soften its attack over the case.

“President Park Geun-hye should personally explain the situation to the people, uncover the truth and punish those responsible, and propose reform plans,” DP chairman Rep. Kim Han-gil said at Monday’s supreme council meeting.

Kim, who called for a special counsel investigation along with Rep. Ahn Cheol-soo, also questioned the credibility of an investigation carried out by the prosecutors’ office.

Kim and Ahn are currently doubling as cochairmen of the committee for launching a new opposition party.

“Results of an investigation by the prosecutors’ office, which is suspected of collaborating with the NIS, will not be trusted by the public. A special counsel investigation is the only answer.”

While Kim stressed the need for an independent probe, Ahn and DP floor leader Rep. Jun Byung-hun called for the dismissal of NIS chief Nam Jae-joon. 

“It would be right to dismiss Nam Jae-joon, who is in charge of the NIS at present,” Ahn said. He also echoed the DP chief in emphasizing the need for an independent probe, saying that the prosecutors’ office was involved in fabricating the evidence.

“The truth needs to be revealed quickly through various means such as an independent probe or a parliamentary investigation.”

By Choi He-suk (cheesuk@heraldcorp.com)