The largely peaceful rallies in Seoul have been growing in size over the past month, attracting an estimated one million people earlier in November, and are among the largest seen in South Korea since the pro-democracy protests of the 1980s
South Korean prosecutors arrested two former top presidential aides Sunday in a snowballing influence-peddling scandal which has seen tens of thousands of people take to the streets to demand President Park Geun-Hye resign.
Park's approval ratings have hit a historic low of five percent -- a record for a sitting president -- over the scandal involving her close friend Choi Soon-Sil.
Choi has been arrested for fraud and also stands accused of meddling in state affairs -- including government appointments and policy decisions -- despite holding no official position.
Ahn Jong-beom, a former senior advisor to Park, was formally arrested early Sunday on charges of abuse of power and attempted coercion, the Yonhap news agency reported.
He is suspected of helping Choi collect millions of dollars in donations from conglomerates like Samsung to two dubious non-profit foundations which Choi set up and allegedly used for personal gain.
Ahn, who has been in custody since Wednesday after stepping down late last month said he would "take responsibility" for failing to properly advise the president, Yonhap reported.
Prosecutors also arrested Jeong Ho-Seong, another former presidential aide, over allegations that he leaked classified information.
The 47-year-old Jeong, who was known as Park's right hand man and has assisted her since 1998, is suspected of passing presidential speeches and official documents to Choi.
Park has been scrambling to restore trust in her administration amid the deepening crisis, reshuffling ministers and senior advisers to bring in figures from outside her ruling conservative Saenuri Party.
But the reshuffle has done little to assuage public anger, with tens of thousands of protesters rallying to demand her resignation in a candlelight demonstration on Saturday.
Police said around 50,000 people had turned out for the rally -- more than double the size of a similar anti-Park protest the week before. Organisers said the number was closer to 200,000.
Han Gwang-Ok, Park's new chief of staff who was appointed last week, said Saturday's protest reflected the gravity of the current situation.
"All senior secretaries must fully cooperate in uncovering the truth beyond any doubt," Han said during a meeting with the presidential secretaries on Sunday.
- Modern-day Rasputin -
In a televised address Friday, Park agreed to be questioned by prosecutors, and sought to portray herself as an over-trusting friend who had let her guard down at a moment of weakness.
Her voice choking with emotion, Park said she had been living a "lonely life" as president and had turned to Choi for company and help.
The South Korean media has portrayed Choi, whose late father was a shadowy religious leader and an important mentor to Park, as a Rasputin-like figure who wielded an unhealthy influence over the president.
Choi is the daughter of late religious leader Choi Tae-Min, who was married six times, had multiple pseudonyms and set up his own cult-like group known as the Church of Eternal Life.
Park has been forced to deny that she fell for a religious cult or allowed shamanist rituals to be performed in the presidential Blue House.
Despite the mass protests, Park is not expected to resign with just over a year of her single term in office left.
Whatever transpires, the very personal nature of the scandal has severely undermined Park's ability to govern, turning her into the lamest of lame-duck leaders at a time of slowing economic growth, rising unemployment and elevated military tensions with North Korea.