South Korea's special prosecutors on Saturday grilled a former health minister as part of their probe into an influence-peddling scandal involving President Park Geun-hye and her friend.

The team of special prosecutors questioned Moon Hyung-pyo, now chief of the National Pension Service (NPS), over suspicion that he exerted pressure on the state fund to back a mega merger deal between top conglomerate Samsung Group's key two units when he was the minister last year. Moon was formally arrested earlier in the day.

He is accused of having pressured the NPS, the biggest shareholder of builder Samsung C&T Corp. to support a controversial merger between it and Cheil Industries Inc. on behalf of the presidential office Cheong Wa Dae.

President Park was impeached on Dec. 9 over a corruption scandal involving her long-time confidante Choi Soon-sil which has rocked the country's politics for months.

State prosecutors earlier said that Park allegedly colluded with Choi to strong-arm Samsung and other local conglomerates into donating money into two non-profit foundations controlled by Choi.

Samsung is suspected of receiving backup from the NPS for the merger deal in 2015 in exchange for donations and favors to Choi and her daughter.

Moon, who had denied of having exerted influence in the pension fund's decision at a recent parliamentary hearing, reversed his statement during an interrogation by special prosecutors, according to the independent counsel team's spokesman Lee Kyu-chul.

Investors are now looking into whether President Park was directly involved in the process, which they believe could constitute bribery.

The team led by independent counsel Park Young-soo arrested without warrant Yi Il-hwa, a professor at Ewha Womans University, on Saturday on suspicion that he gave unjust favors to Choi's only daughter to help her earn credits.

Chung Yoo-ra, Choi's 20-year-old daughter, allegedly gained illicit admission to the university and favors from professors.

Last week, investigators secured a court warrant to arrest Chung, who is believed to be hiding out in Germany.

Choi, currently in custody, is under trial over a set of corruption charges where President Park was named accomplice by state prosecutors.

Park, who denies all charges against her, is waiting for the Constitutional Court's decision over whether to unseat or reinstate her after lawmakers voted to impeach her early this month.

(Yonhap)