By Alex Jensen

SEOUL

 South Korean Prime Minister Lee Wan-koo has offered to resign over a bribery scandal that has rocked the country's political establishment, local media reported Tuesday -- piling further pressure on President Park Geun-hye during her ongoing four-nation South America tour.

Park is expected to accept Lee's decision when she returns to Seoul next week.

Opposition leader Moon Jae-in had announced Monday the start of proceedings to impeach the prime minister over allegations that he accepted a cash bribe in 2013 worth nearly $30,000.

Lee was among several names implicated by a businessman who took his own life earlier this month -- but only after leaving behind a list of names and raising allegations against the prime minister through a newspaper interview.

The president's chief of staff and several ruling party members were also dragged into what has become a snowballing corruption case.

In a written statement from Peru following reports of Lee's resignation, Park urged prosecutors to "clearly shed light on everything by conducting a thorough investigation," national news agency Yonhap reported.

But given her prime minister's claims of innocence and initial determination to keep his job, the president also said she feels his "agony."

Ironically, Lee had begun a campaign against corruption earlier this year.

This latest development represents a public relations blow for Park, who departed for her latest overseas trip on the same day as the first anniversary of one of South Korea's worst-ever maritime disasters.

Frustration with the government's handling of the Sewol ferry tragedy, which saw the loss of 304 lives, boiled over Saturday as protesters clashed with police in central Seoul -- some sprayed vehicles with graffiti calling for the president's resignation.

Park's approval rating slid to 34 percent according to a Gallup Korea poll released Friday.

If she accepts Lee's resignation, she will have to select a third prime minister in just over two years in office. Lee Wan-koo only took up the position in February after a heated confirmation process amid ethical doubts raised by opposition lawmakers.

Deputy Prime Minister Choi Kyung-hwan was reportedly fulfilling Lee's duties Tuesday.