S. Korea's 'female Rasputin' returns to face scandal

With just over a year left to run, Park's presidency has unravelled over shocking revelations that she discussed and sought advice on government policy from Choi Soon-Sil, a close personal friend with no official position and no security clearance.

Choi, who has been holed up in Germany since early September flew into Seoul early Sunday morning on a flight from London, her lawyer Lee Kyung-Jae told reporters.

"Choi told me she will cooperate with the investigation and expressed her deep apology to the people for letting them down and causing them frustration," Lee said.

As well as a public uproar over her relationship with, and apparent control over Park, she faces charges of using her links with the president to strong-arm major companies like Samsung into donating large sums to two non-profit foundations she set up.

Choi has spoken with prosecutors to schedule her questioning, Lee said.

The past week has a seen a daily diet of increasingly sensational media reports regarding Choi, the 60-year-old daughter of a shadowy religious leader and one-time Park mentor.

Invoking a lurid back-story of religious cults, shamanist rituals and corruption, the reports have portrayed Choi as a Rasputin-like figure whose influence extended to vetting presidential speeches and advising on key appointments and policy issues.

'Beyond fantasy'

"As her attorney, I think the case must be thoroughly investigated and the truth be told to prevent any further eruption of speculation that goes beyond fantasy," Lee said.

A public apology by Park, in which she acknowledged seeking limited advice from Choi, has done nothing to assuage public outrage over the president's behaviour or halt a plunge in her approval ratings to record lows.

More than 10,000 people took to the streets of Seoul on Saturday evening, calling on Park to resign and for Choi to be prosecuted. There were similar protests elsewhere, including the country's second largest city, Busan.

Analysts say the scandal could paralyse Park's administration, underling her lame-duck status ahead of presidential elections in December next year.

Choi is the daughter of the late Choi Tae-Min, who married six times, had multiple pseudonyms and set up his own religious group known as the Church of Eternal Life.

Choi Tae-Min befriended a traumatised Park after the 1974 assassination of her mother, who he said had appeared to him in a dream, asking him to help her daughter.

He became a long-time mentor to Park, who subsequently formed a close bond with Choi Soon-Sil that endured after Choi Tae-Min's death in 1994.