The candidates vying to lead South Korea kicked off their official campaigns Monday ahead of a snap presidential election to replace the country's impeached ex-leader, removed over a thwarted martial law bid.

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 frontrunner in an election just four weeks away.

South Korea's former labor minister Kim Moon-soo was reinstated Saturday as his conservative party's presidential candidate -- the same day it revoked his nomination and attempted to replace him with