This article is more than 3 years old

This article is more than 3 years old

South Korea’s president can be investigated in a corruption scandal involving her longtime friend, the prime minister-designate has said.

Kim Byong-joon’s comments came as opposition politicians and activists intensified their demands for prosecutors to investigate Park Geun-hye’s role in the scandal, which has plunged the country into political turmoil. One recent opinion poll had Park’s approval rating at about 9%.

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The national media believe Park’s friend, Choi Soon-sil, controlled the government from the shadows and persuaded businesses to donate millions of dollars to two foundations she controlled.

Prosecutors detained a former senior aide of Park on Wednesday night after summoning him over his alleged involvement in extracting $70m (£57m) in donations, following Choi’s detention this week.

On Thursday, Kim told a televised conference that he thought it was possible to have Park investigated because “all nationals are equal before the law”. But he said the methods of any such inquiry into the head of state must be carefully done.

Kim, a public administration professor, served as a senior policy adviser for the late liberal president Roh Moo-hyun. Park’s nomination of Kim for the country’s number two job was seen as an effort to garner support from liberals.

The prospect of parliamentary approval for Kim’s nomination is unclear as the main opposition, the Democratic party, described it as a tactic to divert attention from the scandal.

Park may survive what has become the most difficult period of a turbulent four years in office. However, if she is forced to name a prime minster chosen by the opposition, it will hamstring her authority and may end her ability to govern.

Much of the public frenzy over the scandal is linked to Choi’s family. Her father led a religious cult and reportedly was a mentor for Park, whose parents were assassinated in the 1970s. Park’s father was a military dictator who ruled South Korea for 18 years.