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.

South Korea's Supreme Court will issue a ruling on Thursday in a case involving presidential frontrunner Lee Jae-myung, which could disqualify the former opposition party leader from contesting the country's June 3 election.