The Prime Minister's Office said Monday it will refer four of its staff members for prosecution investigation on suspicion of illegal surveillance of a civilian.
Lee In-kyu, a senior official in charge of investigating ethics-code violations by public officials, and three lower-level officials, have been found to have violated the code of conduct as a result of the office's internal probe, the office said.
The office has come under fire over allegations that its officials conducted unlawful surveillance of a civilian who posted a video critical of the government on a Web site in 2008.
The main opposition Democratic Party is intensifying its attack on the government, calling for the launch of a parliamentary investigation into the case.
"We'll ask the prosecution to look into the allegations, feeling the need to clearly find truth with them," Cho Won-dong, a vice minister-level official at the office, told reporters.
The four are suspected of misusing their power and interfering with the civilian's business as well as being involved in other illegalities, he added.