Leaders of a South Korean left- leaning party offered public apology Friday for the failure to expel two lawmakers allegedly involved in a rigged party primary.

The two lawmakers of the Unified Progressive Party, Lee Seok-ki and Kim Jae-yeon, were elected in the April general elections as proportional representatives, but have been under pressure to resign following revelations of vote-rigging attempts during the primary.

The fledgling party, beset by infighting between supporters and foes of the two newbie legislators, held a meeting Thursday to decide on their fate only to decide not to oust them.

The decision to retain their membership highlighted the influence of a faction known for pro-Pyongyang views, which both Lee and Kim reportedly share, and led many supporters to renounce the party.

Reform-minded party members, including chairman Kang Ki-gab and floor leader Shim Sang-jung, publicly apologized for the controversial decision that observers say further delegitimized the leftist party in the eyes of the public.

"Progressive politics have lost its direction," Kang said in a press conference. "We've committed another sin (by letting down) the public and the supporters."

Shim, who offered to step down as the floor leader after the powerful pro-Pyongyang faction voted down the expulsion motion, also apologized in a press conference for "failing yet again to meet the public's expectations."

The leftist party was founded last year through a merger among three progressive parties. Its new-found status as the third largest party in the 300-member parliament was considered a major success.