South Korea’s president is engulfed in a political scandal with plotlines straight out of a soap opera: rumors of secret advisers, nepotism and ill-gotten gains. Updated on Nov. 21. (Anna Fifield, Yoonjung Seo, Jason Aldag/The Washington Post)

South Korean President Park Geun-hye suffered a heavy blow Sunday when prosecutors indicted a friend of hers on charges including extortion and abuse of power, and indicated they thought the president was complicit in the crimes.

The prosecution said it would continue to try to question Park, with the announcement effectively making her a suspect rather than a witness, while opposition leaders said they would redouble their efforts to force Park from office.

“There are now sufficient grounds for her impeachment,” Moon Jae-in, a prominent opposition politician and presidential hopeful, said after the announcement.

It came a day after hundreds of thousands of South Koreans took to the streets of central Seoul for a fourth consecutive Saturday, calling on Park to resign. The demonstrations are the largest since South Korea democratized in 1987.

The prosecution said Sunday that it had indicted Choi Soon-sil, a Park friend of 40 years who held no official position, with abuse of power, coercion, attempted coercion and fraud. It also indicted two former presidential secretaries on charges including abuse of power, attempted coercion, fraud and divulging classified information.

At a Nov. 18, 2016 rally in Seoul, protesters wearing masks of South Korean President Park Geun-hye, left, and Choi Soon-si call on the president to step down. (Ahn Young-Joon/AP)

The charges come out of a corruption and influence-
peddling scandal that has Park, South Korea’s first female president, fighting for her political life.

A famously aloof person, Park is accused of relying on Choi for everything from policy advice to wardrobe choices, instead of seeking counsel from her aides. Choi, the daughter of a shamanistic cult leader, is accused of exploiting those ties to raise money and win favors for herself and her family.

Sunday’s charges relate to Choi’s alleged extortion, with the help of one of the presidential secretaries, An Chong-bum, of $70 million from 53 companies through a big-business lobbying group, the Federation of Korean Industries. The companies felt they had to donate the money or they would be at risk of audits or unfair treatment from government authorities, prosecutors said.

The money was meant for two foundations, but Choi is alleged to have siphoned off much of it for her personal use.

The other presidential aide, Chung Ho-sung, leaked at least 180 government documents to Choi over three years, including 47 that included confidential information such as the appointments of ministers, prosecutors said.

Based on cellphone records and notes containing instructions from Park about raising funds for Choi’s two foundations, the prosecution concluded that Park “played a large role” in the efforts to raise money from the businesses, said Lee Young-ryeol, chief of the investigation at the prosecutors’ office, during a news conference Sunday in Seoul.

Although the president cannot be charged while in office, Lee said prosecutors would continue to investigate Park and her actions, voicing confidence that they could prove that she was an accomplice. Charges could be brought against her once she leaves office.

Park was supposed to be questioned by prosecutors last week but instead hired an attorney, who asked for more time to prepare and for the interrogation to be in written form, rather than in person. The attorney said that Park would “try to cooperate” with prosecutors this week.

Park’s spokesman, Jung Youn-kuk, said Sunday that it was “regrettable” that the prosecutors claimed the president had committed crimes, saying the results announced Sunday were not only false but were also “based on imagination and speculation rather than objective evidence.”

“The president does not see the prosecutors’ investigation as fair and hopes these unproven allegations will not be exploited by politicians,” Jung said.

But opposition leaders seized on the results of the investigation. Eight potential presidential candidates met Sunday to discuss how to push for impeachment.

“President Park has now become a suspect, creating the legal conditions to table a motion for her impeachment,” Youn Kwan-suk, the spokesman for the main opposition Democratic Party, told reporters.

“She should follow people’s demands through a decision to resign voluntarily rather than making the worst choice that would plunge the nation into a bigger crisis,” he added, according to the Yonhap News Agency.

As the scandal has rumbled on, some politicians have been hesitant to move to impeachment proceedings because the lengthy legal procedures could take as long as eight months. As Park has only 14 months left in office, they have instead called on her to step down.

Opposition parties lack the seats needed to impeach a president, which requires two-thirds of the National Assembly. However, if some of Park’s critics from her own Saenuri Party join with the opposition to vote for impeachment, the two-thirds figure might be achievable.

Park has been digging in, apparently in the hope that she can ride out the scandal. After last weekend’s huge protest in central Seoul, her spokesman said that Park was “earnestly considering ways to normalize state affairs and fulfill her responsibility as the president.”

Even before Sunday’s announcement, analysts at Eurasia Group, a consulting firm that focuses on political risk, were putting the chances of her leaving office early at 70 percent.

“The longer Park tries to hold out, the stronger popular demands for her removal will grow, increasing pressures on opposition parties to seek to impeach her,” Eurasia’s Scott Seaman wrote in a note.

Yoonjung Seo contributed to this report.