South Korea's third acting leader in five months, Lee Ju-ho, is an understated labour economist and education bureaucrat thrust into managing high-stakes trade talks with the United States and a country reeling from political knife fights before a crucial election.

Han, who briefly served as acting leader following President Yoon Suk-yeol's impeachment over a controversial martial law declaration, said he would push for constitutional amendments to better balance power between the president and parliament.

Democratic Party nominee Lee Jae-myung will be retried on electoral violation charges, while the acting president has resigned and is expected to enter the race.