SEOUL - South Korea's presidential office said on Saturday it was cooperating with prosecutors'investigation into key aides to President Park Geun-hye over allegations an old friend of hers enjoyed inappropriate influence over her.
Prosecutors' request for presidential Blue House documents came ahead of an evening protest expected to draw thousands in central Seoul calling for Park's resignation amid a scandal that has cast her presidency into crisis.
Park's office said late on Friday she had ordered her senior secretaries to tender their resignations, and she will reshuffle the office in the near future. Her chief of staff separately offered to resign earlier, the office said.
The deepening crisis over allegations that Park's friend, Choi Soon-sil, enjoyed inappropriate influence over her has sent her public support to an all-time low, with more than 40 per cent in an opinion poll saying Park should resign or be impeached.
Prosecutors are investigating two aides to Park who allegedly helped Choi get access to drafts of Park's speeches and set up two foundations with about 50 billion won ($44 million) in contributions from conglomerates that she later benefited from, South Korea's Yonhap news agency reported.
Opposition parties have demanded a thorough investigation but have not raised the possibility of impeaching the president.
A public apology from Park on Tuesday for giving Choi access to draft speeches during the first months of her presidency has done little to deflect demands that Park reveal the full nature of her ties with Choi and whether the friend enjoyed favours.
Up to 4,000 people were expected to attend a rally organised by a group of left-leaning civic groups later on Saturday in central Seoul, but the number could be larger as other citizens were likely to join, Yonhap said, citing a police source.
Park, in the latter part of a single five-year-term presidency, is the latest South Korean leader to become engulfed in scandal involving family or friends.
Civic groups and students have called for her to step down, and for criminal charges to be brought against her aides and others who helped release government documents to Choi.