South Korean ambassador to Australia, Lee Jong-sup, attends a meeting held at the Ministry of Foreign Affairs in Jongno, central Seoul, on Monday. (Yonhap)

Lee Jong-sup, South Korea’s ambassador to Australia, on Friday has given up the post less than a month after he was appointed.

The former national defense minister’s offer to step down follows a controversy over his his taking on the job while still under investigation over the death of a marine in July last year.

President Yoon Suk Yeol approved his resignation later the same day, according to his press office.

Twenty-year-old Corporal Chae Su-geun died when he was swept away by an overflowing stream during a search and rescue operation to locate missing people amid record heavy rainfall in Yecheon County, North Gyeongsang Province, last July 19.

Chae’s death sparked criticism that his superiors had forced him to push ahead with a risky operation without proper safety measures in place.

The Corruption Investigation Office for High-ranking Officials had been looking into allegations that Lee, as then-national defense minister, had exerted influence to hold off the findings of an internal probe by the Marines into Chae’s death.

The CIO had imposed a travel ban on Lee, which the Justice Ministry had lifted March 8, amid the controversy over his appointment.

The disgraced ambassador said in a statement released to the press that he submitted his letter of resignation to the Ministry of Foreign Affairs in Seoul on Friday.

In the statement, he said he has been asking the CIO for a “swift investigation into the matters.” He said he would stay in Seoul and “respond to the remainder of the procedures diligently.”

“To that end, I have written to the Ministry of Foreign Affairs to express my intention to resign as ambassador to Australia. I ask the ministry to accept my offer to resign.”

Yoon’s appointment of Lee as the top envoy to Australia has been cited by political observers in Korea as a major reason behind the ruling People Power Party’s plunging ratings.

Polls in the last two weeks have showed the People Power Party lost its lead over its rival, the main opposition Democratic Party of Korea, falling behind even in districts that are traditionally conservative strongholds.

The general election to fill the next National Assembly is on April 10.