Choi has denied allegations that she used her friendship with Park to strongarm companies like Samsung into donating large sums to non-profit foundations that she then used for personal gains, Yonhap said.

Ahn is suspected of helping Choi collect the dubious donations.

“The president herself understands well the gravity of the situation”, Justice Minister Kim Hyun-woong told parliament Thursday, Yonhap reported.

“Depending on where the ongoing investigation leads, I will consider whether it is necessary and legally possible to investigate (Park) to find truth,” he said.

South Korea’s new prime minister nominee Kim Byong-joon said on Thursday it is his view that the country’s president can be subject to prosecutors’ ongoing investigation into an influence peddling scandal.

“My position is an investigation is possible. But since (she) is the head of state, its process and method requires circumspection,” he said.

However, under South Korea’s constitution, the incumbent president may not be charged with a criminal offence except for insurrection or treason.

But it is not clear whether the sitting president can be probed by prosecutors and then charged after they leave office.

In an effort to deflect rising public criticism, Park had been urged to create a neutral cabinet by bringing in members from outside her ruling conservative Saenuri Party.

On Thursday, she announced her pick for chief of staff, Han Gwang-ok, a former aide to late President Kim Dae-jung, in an appointment the presidential Blue House said would help get the rattled administration back on track.

The 74-year-old veteran politician, a long serving liberal who switched sides and joined Park’s administration in 2013, has dedicated his life to “democracy and national reconciliation”.

“He is well suited to assist the president from the citizens’ perspective,” presidential spokesman Jung Youn-kuk said.

Park has also reached across the traditional political divide with a host of new appointments, including tapping a liberal politician as her new prime minister - a largely symbolic post.

But the opposition has dismissed the reshuffle as a smokescreen, calling for a full investigation of Park’s relationship with Choi and vowing to block the new prime minister’s nomination by wielding their combined parliamentary majority.

The media has portrayed the 60-year-old Choi as a Rasputin-like figure, who wielded an unhealthy influence over Park that continued after her presidential election victory in December 2012.

Choi is the daughter of late religious leader Choi Tae-min, who was married six times, had multiple pseudonyms and set up his own cult-like group known as the Church of Eternal Life.

He befriended a traumatised Park after the 1974 assassination of her mother - whom he said had appeared to him in a dream. Park treated him as a mentor and subsequently formed a close bond with his daughter.

Choi flew back to Seoul Sunday from Germany to submit to herself for questioning, saying after she fought her way through a scrum of press and protesters that she had “committed a deadly sin,” Yonhap reported.

Prosecutors are seeking a warrant to formally arrest Choi - who they have deemed a flight risk and “unstable” - before the emergency detention period expires.

The scandal comes as South Korea, Asia’s fourth largest economy, faces slumping exports and high unemployment amid rising nuclear and missile threats from North Korea.

Additional reporting by Reuters