The main accused in a huge domestic corruption scandal in South Korea that led to massive protests in the country and impeachment of the country's president, pleaded not guilty during the first formal hearing in the case Thursday.

The hearing followed two preparatory hearings held in December, where Choi Soon-sil, 60, a close friend of the South Korean president was charged with abuse of power and attempted fraud.

Choi, dubbed the "Korean Rasputin", has been in custody since early November, and denied all the charges against her, calling them "unjust," reported South Korean news agency Yonhap.

Choi is also charged with interfering in State matters, despite not holding any public office and of having pressurized large companies, including Samsung, to donate huge sums of money to nonprofit foundations headed by her.

An Chong-bum and Jeong Ho-seong, two former close aides of President Park Geun-hye, also attended the hearing, in what was their first public appearance since they were arrested in December.

An is accused of helping extort from the conglomerates some 77.4 billion won (nearly $65.3 million) for two foundations - of which Choi was de facto head - part of which she (Choi) may have later appropriated for personal use, while Jeong is accused of having handed over official and presidential documents to Choi.

An denied the charges and said he will press ahead with his defense in upcoming hearings, while Jeong's lawyer did not clarify his client's stance, alleging he could not review the case owing to a raid by investigators in his prison cell.

A team of investigators had raided the Seoul and Uiwang detention centers where Choi and the other two suspects have been lodged since their arrest.

The first public hearing in the case is scheduled for Jan. 17.