South Korea’s embattled conservative party has taken the unprecedented step of nullifying its primary and replacing presidential candidate Kim Moon Soo with former Prime Minister Han Duck-soo, just one week after Kim’s selection.

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.

A Seoul court on Friday ruled the main conservative party could hold another convention to agree a presidential candidate amid a bitter dispute over who should represent the party in the June 3 election.