The main opposition Democratic United Party (DUP) alleged Monday that then President Lee Myung-bak ordered the country's national spy agency to post illegal political comments on the Internet ahead of last year's presidential election.

Following a four-month-long probe, police said last week that two employees of the National Intelligence Service were found to have posted the comments on behalf of the agency in a bid to influence the tight presidential race.

However, the online activities were not deemed to be serious enough to charge the suspects with violating a law banning public officials from participating in election campaigns. Prosecutors are now looking into the case.

"(This case) has revealed ... that then NIS chief Won (Sei-hoon) directly instructed (the employees) to illegally intervene in politics during the presidential election," DUP spokeswoman Rep. Kim Hyun said during a press briefing.

Recalling that Won gave private weekly briefings to Lee at the time, the spokeswoman said there are questions as to whether he reported on the "political maneuverings" and received specific instructions to carry them out.

"(Won) should reveal the truth regarding under whose orders he carried out the political maneuverings, ask for forgiveness from the public and take legal responsibility," she said.

President Park Geun-hye should clearly state her position on the scandal and hold a news conference related to it, she added. (Yonhap News)