Lee Jae-myung, leader of the main opposition Democratic Party, speaks during a party Supreme Council meeting at the National Assembly on Wednesday. (Yonhap)

Opposition leader Lee Jae-myung on Wednesday stepped up criticism of President Yoon Suk Yeol for vetoing a bill mandating a special counsel investigation into the military's response to a Marine's death and urged the ruling party's cooperation in repassing the bill.

Lee, leader of the main opposition Democratic Party, made the demand during a party Supreme Council meeting, saying the ruling People Power Party should "break away" from what he described as "bad politics that turns a blind eye to the death of a citizen."

"If the People Power Party continues to act as defenders of the president and denies the will of the people, they will be recorded in history as accomplices of an atrocious government," Lee said.

On Tuesday, Yoon exercised his veto power, the 10th time in his two years in office, by approving a motion demanding parliamentary reconsideration of the bill that was railroaded through the opposition-controlled National Assembly on May 2.

The bill calls for a special counsel to look into allegations Yoon's office and the defense ministry inappropriately interfered in the Marines' investigation into the death of Cpl. Chae Su-geun, who was killed during a search mission for victims of heavy downpours in July 2023.

Meanwhile, the People Power Party has hit back at the opposition, taking issue with a solo visit by former first lady Kim Jung-sook, wife of former president Moon Jae-in, to the Taj Mahal in India in 2018.

Kim's visit drew controversy over whether she was officially invited and for using public funds worth 400 million won ($278,940). It was the first time in 16 years that a South Korean first lady had made a foreign visit without the president.

Members of the People Power Party have called for a special counsel probe into Kim, which the Democratic Party has accused as an attempt to "water down" issues regarding allegations that the current first lady Kim Keon Hee illegally received a luxury handbag as a gift in 2022. (Yonhap)