South Korea's main opposition party on Tuesday picked its former campaign chief, Kim Chong-in, as its caretaker leader, but the veteran politician virtually rejected the decision, taking issue with its failure to guarantee an extensive term.

The United Future Party (UFP), reeling from the shock of a crushing parliamentary election defeat, convened its National Committee and approved the nomination of Kim as head of the party's interim leadership committee.

But the party failed to hold the Standing National Committee to revise its constitution, under which it must hold a national convention to elect a new leader by the end of August, so Kim would have to quit by then.

Kim led the UFP's campaign for the April 15 general elections.

"The remaining issue is whether Kim will work as a manager-style chairman of the emergency committee until Aug. 31. His position is that he won't do so," Choi Myung-gil, a key aide to Kim, said.

Kim apparently wants to head the party through the spring of next year in order to wield clout in the process to select its candidate to run in the 2022 presidential election.

In a media interview last week, Kim said he would accept the UFP's proposal on the condition that it guarantee an open-ended term and power equivalent to that of a regular party chairman.

Shortly after the committee meeting, Rep. Shim Jae-chul, the UFP's floor leader, told reporters, "(I plan to) tell the details of the vote to Kim again and ask him to accept the post ... I hope he will accept."

Kim has engaged in campaigning and crisis management in both conservative and liberal parties during his decadeslong career.

In the recent election seen as a referendum on President Moon Jae-in, the main opposition and its satellite party managed to secure only 103 seats in the 300-seat parliament. The liberal Democratic Party (DP) and its affiliate party won 180 seats.

Former UFP chief Hwang Kyo-ahn immediately stepped down after losing to DP heavyweight and former Prime Minister Lee Nak-yon in a key constituency in Seoul. (Yonhap)