The main opposition Democratic Party (DP) demanded Thursday President Park Geun-hye apologize over allegations that her ruling party mobilized the state spy agency to win last year's presidential election.

The demand comes amid growing allegations that the National Intelligence Service (NIS) could have strong ties to the ruling Saenuri Party. Last year, the NIS was accused of conducting an online smear campaign to sway public opinion in favor of the ruling party ahead of December's presidential election.

This week, the NIS declassified and disclosed a summit transcript containing late South Korean President Roh Moo-hyun's controversial remarks on the disputed Yellow Sea border with North Korea.

The opposition party has accused the spy agency of divulging state secrets in an attempt to divert public outrage away from the scandal involving the alleged smear campaign.

An opposition lawmaker fueled the controversy Wednesday, claiming that a key official of Park's then election campaign had already had access to the classified document before the election and planned on disclosing it if his party won the race.

"(Park) should apologize to the public as soon as she returns (from China) for the Saenuri Party's political maneuvers during the presidential election, which were manipulations of the law," DP Chairman Rep. Kim Han-gil said during a general meeting of party lawmakers.

Park left for China earlier in the day for a four-day visit that will include a summit with Chinese President Xi Jinping.

"President Park should promise the people that she will conduct sweeping reforms of agencies of power such as the NIS, the prosecution and the police to establish political neutrality and turn them into agencies that properly serve the people," Kim said. "For this, the DP will gather all of its strength and fight together with the people." (Yonhap News)