SEOUL, Dec. 1 -- South Korea is embroiled in a scandal on the behind-the-scene power to President Park Geun-hye after a local daily newspaper reported that a former aide to Park intervened in state affairs though he has no official position in the government.

Prosecutors reportedly launched an investigation into the case Monday as the presidential office filed a libel suit against the media.

The newspaper Segye Times reported Friday that Jeong Yun-hoe, 59, has met with presidential secretaries twice a month since October last year and has been briefed by them on state affairs. Jeong was an aide to Park in late 1990s when she was a lawmaker.

It cited an internal document written by a presidential official on Jan. 6. According to the document gained by the newspaper, Jeong talked with three presidential secretaries about how to oust Kim Ki-choon, the incumbent chief of staff to President Park.

The internal report also described the alleged 10 heavyweights under President Park as the so-called 10 eunuchs.

President Park said during a meeting of senior presidential secretaries that the case is an act of undermining the nation's foundation, calling for a thorough investigation into it.

"It's a problem to report as if there was any unofficial line or powerful figure behind the scenes without checking with related people," Park said, noting that it can be verified easily by checking with the people.