The National Intelligence Service is coming under increasingly heavy fire from the political arena as the prosecution’s investigation speeds up.

On Monday, the prosecution raided the NIS, hours after President Park Geun-hye called for a thorough investigation into the allegations of evidence fabrication.

The prosecution is reportedly analyzing confiscated materials and questioning NIS agents linked to the case. The NIS agents implicated, said to number four or five, were banned from leaving the country last week.

The NIS is accused of forging evidence against former Seoul City official Yoo Woo-seong, who is suspected of spying for North Korea.

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

The documents, provided by the NIS, were later claimed to be forgeries, while a Korean-Chinese NIS collaborator testified that the spy agency offered him money to provide the forged documents.

Despite the speedy actions of the prosecution, the main opposition Democratic Party did not let up its barrage and repeated its calls for the dismissal of NIS chief Nam Jae-joon and for the launch of a special counsel investigation.

“The starting point for resolving the issue is the immediate dismissal of Nam Jae-joon and a thorough probe through a special counsel investigation,” DP floor leader Rep. Jun Byung-hun said.

“The president not taking responsibility nor seeking out (those responsible) is clear dereliction of duty and ignoring the public opinion.”

Rep. Moon Byeong-ho added his voice, saying that the developments between Sunday’s apology from the NIS to Monday’s raid appeared to be being played out according to “a well-formulated scenario.”

“This case should be investigated not by the prosecution but through a special counsel probe to uncover the truth and to punish those involved,” said Moon, DP chief on the parliamentary committee on NIS reform.

Moon also said that individuals found guilty of forging evidence and of espionage should be treated on equal terms, citing the National Security Act.

Under the act, those found guilty of forging evidence with the intent to frame others for espionage can be sentenced to death, life imprisonment or a prison sentence of more than seven years.

The ruling Saenuri Party lawmakers, who usually adhere closely to the party’s official stance, are expressing divided views.

“(Calling for a special probe) is nothing more than foul political attack aimed at clouding the nature of the case and hampering the investigation,” Saenuri Party supreme council member Rep. Yoo Ki-june said.

Others, however, approached the issue with caution while some even echoed the DP’s demands.

“Nam taking responsibility for the forgery scandal and stepping down would be the right way for a civil servant,” five-term lawmaker Rep. Lee Jae-oh of the ruling party wrote on his Twitter account.

“(Nam stepping down) would be a suitable response to the president’s comments,” Lee wrote, referring to the president’s statement that the situation was regretful.

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