SEOUL, South Korea >> South Korean prosecutors said they believe President Park Geun-hye conspired in criminal activities of a secretive confidante who allegedly manipulated government affairs and exploited her presidential ties to amass an illicit fortune — a damning revelation that may convince opposition parties to push for her impeachment.

Prosecutors are planning to soon question Park, who has immunity but can be investigated, said Lee Young-ryeol, chief prosecutor of the Seoul Central Prosecutors’ Office.

Prosecutors on Sunday formally charged Park’s longtime friend, Choi Soon-sil, on suspicion of interfering with state affairs and bullying companies into giving tens of millions of dollars to foundations she controlled.

In a televised news conference, Lee said that based on the evidence, “the president was involved as a conspirator in a considerable part of the criminal activities by suspects Choi Soon-sil, Ahn Jong-beom and Jung Ho-sung.” He was referring to two presidential aides who also were formally charged Sunday for allegedly helping Choi.

“However, because of the president’s impunity from prosecution stated in Article 84 of the constitution, we cannot indict the president. The special investigation headquarters will continue to push for an investigation of the president based on this judgment,” Lee said.

Park is facing growing calls to resign over the scandal critics say has undermined the country’s democracy. Emboldened by huge protests in recent weeks, opposition parties have been stepping up pressure on Park to quit.

Opposition parties have so far refrained from seriously pushing for Park’s impeachment over fears of triggering a backlash from conservative voters and negatively impacting next year’s presidential election.

However, there are growing voices within the opposition saying that an impeachment attempt is inevitable because it’s unlikely Park will resign and give up her immunity.

Ahn Jong-beom, Park’s former senior secretary for policy coordination, has been under suspicion of pressuring companies into making large donations to foundations Choi controlled.

Jung Ho-sung, another former presidential aide who was also indicted, has been accused of passing on classified presidential documents to Choi, including information on ministerial candidates.

Prosecutors are also seeking to indict Cha Eun-taek, a famous music video director who allegedly used his close relationships with Choi to win lucrative government culture projects, and former vice sports minister Kim Chong, suspected of providing business favors to sports organizations controlled by Choi.

Kim is also under suspicion of influencing the ministry’s decision to financially support a sports foundation run by Choi’s niece, who prosecutors detained on Friday.

On Saturday, police said about 170,000 people turned out for the latest anti-Park protest in streets near City Hall and a boulevard fronting an old palace gate in Seoul.

Demonstrators also marched in streets near the presidential offices, carrying candles and illuminating cellphones, and shouting “Park Geun-hye step down” and “Arrest Park Geun-hye.”

Park’s term lasts until Feb. 24, 2018. If she steps down before the presidential vote on Dec. 20, 2017, an election must be held within 60 days.