More than 400 people attended a special mass held by Catholic priests on Friday urging President Park Geun-hye to step down, just hours after the presidential office expressed displeasure at their move.

Members of the left-leaning Catholic Priests' Association for Justice gathered in the southwestern city of Gunsan for the mass demanding Park take responsibility for the state agencies' alleged intervention in last year's presidential race to sway the election in her favor.

"We can only conclude that a president who ignores people's demand for the truth and displays characteristics of a stubborn dictator is acknowledging that she is no longer the president chosen by the people of Korea," the priests said.

The presidential office Cheong Wa Dae had expressed disapproval after learning of the plans for the mass.

"A prayer is to wish for the best and pray for blessing. Urging a president elected by the people to resign isn't wishing for the best," senior presidential press secretary Lee Jung-hyun told reporters earlier in the day. "For the past 10 months, the president has given her all for the happiness of the people. I ask for support and help for the president."

The scandal, which began nearly a year ago, centers on allegations that state agencies, including the National Intelligence Service (NIS), attempted to influence the tight presidential race with online political postings in favor of Park, the ruling party candidate at the time.

The case has gained traction as fresh allegations have emerged one after another in recent weeks that the alleged state meddling was much more extensive than originally thought.

Park has categorically denied any link to the scandal, saying she neither had any knowledge of the agency's alleged wrongdoing nor did she benefit from it.

The spy agency has also claimed the online activity was part of its routine anti-North Korea psychological warfare. (Yonhap News)