South Korean lawmakers failed to hold a hearing at a detention center with key suspects in a scandal involving President Park Geun-hye on Monday.

Members of a special parliamentary committee visited a detention facility on the outskirts of Seoul to question Park's confidante Choi Soon-sil, and former presidential aides Ahn Jong-beom and Jeong Ho-seong, who had refused to attend a hearing at the National Assembly this month.

The three figures were summoned to a hearing at a meeting room Monday but again refused to appear, claiming their testimonies could affect an on-going investigation by independent prosecutors.

There is no legal grounds to force witnesses to attend a parliamentary hearing.

The committee said it decided to file complaints against them on charges of contempt of the National Assembly.

The panel has held five sessions of inquiry, summoning presidential staff members, business tycoons and other figures involved in the influence-peddling scandal.

Choi allegedly exerted influence on 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 ($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)