South Korea's conservatives dropped their presidential candidate on Saturday and reopened the nomination process, after the former prime minister decided to join the party to challenge the liberal front-runner in an election just four weeks away.

The People Power Party said its leadership decided to cancel the nomination of Kim Moon-soo and hold a new vote on replacing him with former Prime Minister Han Duck-soo, whose late entry into the race derailed the consensus over its candidate for the snap June 3 presidential vote.

The liberal Democratic Party's candidate Lee Jae-myung has been a clear front-runner to replace conservative former President Yoon Suk Yeol, who was removed from office in April for violating his duties when he declared a short-lived martial law in December.