Lee Jae-myung has been the front-runner in South Korea's presidential election, but his candidacy has been complicated by criminal trials he has decried as politically motivated.

South Korea's former President Yoon Suk Yeol is to be additionally charged with abuse of authority. The ex-president is already being tried for insurrection, over his failed bid to impose 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.