Prime Minister Han Duck-soo has been mulling whether to run for election, while the main opposition candidate and front-runner suffered a setback in court.

South Korea's top court cast doubt on Thursday on frontrunner Lee Jae-myung's eligibility to run for the presidency, while the resignations of the prime minister and finance minister shook the interim government in place since December's martial law.

South Korea's former prime minister Han Duck-soo announced his bid for the presidency on Friday, joining the race in a snap election triggered by the impeachment of ex-president.The June 3 vote will decide who replaces impeached former president Yoon Suk Yeol,