South Korean lawmakers plan to visit a detention center Monday to question key suspects in a scandal involving President Park Geun-hye, who have refused to attend a hearing at the National Assembly.

The special committee seeks to hold a hearing with Park's confidante Choi Soon-sil, who is in custody at a detention facility on the outskirts of Seoul, at 10:00 a.m. and Ahn Jong-beom, former senior presidential secretary for policy coordination, and Jeong Ho-seong, former secretary for private presidential affairs, later in the day.

But observers said the committee's visit may end in vain. The three figures had said they would not attend the hearing, saying their testimonies could affect an on-going investigation by independent prosecutors. There is no legal ground to force witnesses to attend a parliamentary hearing.

The special committee hosted five sessions at the parliament this month, summoning presidential staff members, business tycoons and other figures involved in the influence-peddling scandal.

Choi allegedly exerted power over state affairs without any government position and used her ties with the president to extort money from businesses.

During an interrogation by special prosecutors Sunday, Choi denied new allegations that she stashed around 10 trillion won (US$8.29 billion) abroad. She told investigators that she would donate all the money to the state, if there were any such money, according to the independent counsel team.

Local media reported Choi may have hidden 800 billion won in Germany and more in other European countries via her ghost companies.

The independent counsel on the scandal said the team has hired a former state tax agency official to trace Choi's assets at home and abroad.

Choi and Ahn are suspected of forcing conglomerates to donate 77.4 billion won to the Mir and K-Sports Foundations, which she virtually controlled.

Sources said that the team will also track down dubious assets Choi's family amassed over the past 40 years.

Choi is the fifth daughter of Park's late mentor Choi Tae-min.

The late Choi, who used to lead a religious cult, had reportedly advised Park since her mother, Yook Young-soo, was assassinated by a North Korea sympathizer in 1974.  (Yonhap)