President Park Geun-hye called Monday for a thorough probe into allegations that a former aide with no position in the government interfered in state affairs.

The move came three days after the Segye Times, a local newspaper, reported that Jeong Yun-hoe, who served as chief secretary to Park during her term in parliament, tried to mastermind a plot to oust Kim Ki-choon, the current chief of staff to Park, citing an internal document from the presidential office dated Jan. 6.

Jeong holds no official title in the Park administration, though he regularly met with incumbent presidential secretaries and received briefings from them, according to the report.

Park condemned the leak of the internal document.

"I think it's problematic for (media) to suggest there was suspicion by reporting as if there were an unofficial line or a powerful figure behind the scenes without checking with related people," Park said in a regular meeting with her aides.

Park also called on prosecutors to shed light on the case and instructed her aides to cooperate with the probe to determine the circumstances behind the leak.

She warned of harsh punishment for any officials who are found to have committed inappropriate behavior, regardless of their title.

"If there is any malicious slander, those responsible for it will he held accountable," Park said.

The presidential office has denied the allegations and lodged a complaint with the prosecution against the daily for libel.

Jeong's lawyer, Lee Kyung-jae, dismissed the allegations as "groundless" and said he plans to explore all legal actions against media reports on Jeong.

Also Monday, Park called for structural reform of the country's economy to ensure sustainability. She said next year is the right time to press ahead with structural reform as 2015 will be a year without elections.

Park's single five-year term ends in early 2018, and by law, she cannot seek re-election. (Yonhap)