South Korea's president bowed before issuing a grovelling nine-minute apology over a bizarre political scandal involving a shadowy female aide with links to a cult.

Park Geun-hye trembled as she admitted tragedy and 'loneliness' drove her to rely on old friend Choi Soon-sil, who is thought to have edited some of her speeches.

Choi, whose father is accused of leading a religious cult, is feared to have meddled in key policy and personnel decisions - despite not working for the government.

During her speech today, Park denied speculation she had started worshipping cult religions or that shamanistic rituals were held at the presidential Blue House.

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South Korean President Park Geun-hye bowed before issuing a grovelling nine-minute apology over a bizarre political scandal

'I feel a huge responsibility (for the scandal) deep in my heart,' Park said, her voice shaking during the high-stakes TV address to the nation.

'It is all my fault and mistake.'

The president also discussed her friendship with the mysterious woman at the heart of the scandal - Choi.

'I put too much faith in a personal relationship and didn't look carefully at what was happening,' Park said.

'Sad thoughts trouble my sleep at night. I realize that whatever I do, it will be difficult to mend the hearts of the people, and then I feel a sense of shame and ask myself, 'Is this the reason I became president?''

Park Geun-hye trembled as she admitted tragedy and 'loneliness' drove her to rely on old friend Choi Soon-sil, who is thought to have edited some of her speeches

Choi (both) and a former presidential senior secretary were arrested over claims they pressured companies into making large donations to two foundations

Choi and a former presidential senior secretary were arrested over claims they pressured companies into making large donations to two foundations and that Choi misused some of the funds.

Park vowed to accept a direct investigation into her actions, but the opposition immediately threatened to push for her resignation.

'Anyone found by the current investigation to have done something wrong must be held responsible for what they have done, and I am also ready to face any responsibility,' she said.

Her friendship with Choi was born out of family tragedy. Park's mother was assassinated in 1974 by someone trying to kill her father, dictator Park Chung-hee.

Choi's father, a shadowy religious figure named Choi Tae-min, emerged around the same time as Park's mentor. Her father was assassinated five years later.