The four co-leaders of Korea's left-wing minor party resigned en masse over allegations of wide-scale election fraud in the selection of proportional candidates in last month's parliamentary race.

Lee Jung-hee, one of the Unified Progressive Party (UPP) leaders and figurehead for the East Gyeonggi Coalition, the dominant faction in the party, stepped down ahead of the critical central committee meeting that has been convened to chart future actions.

She told party members that there is a need for harmony so the UPP can be reborn and receive the trust of the people.

"I have been able to overcome past adversities because of the help of party members," the party leader said.

Her resignation was followed immediately by the stepping down of Shim Sang-jung, Rhyu Si-min and Cho Joon-ho, who are all co-chairs of the party. Cho headed the two-week internal probe that allegedly discovered widespread voting irregularities.

In-house probes revealed that a computer program used for internal online ballots had been changed several times and technical errors occurred, leading to the suspension of votes and undermining the credibility of the online ballots.

The party also admitted votes had been cast en masse through a single Internet Protocol address, an indication of voting irregularities. The IP address, the online equivalent of a street address or a phone number, should be different for each voter.

The country's public prosecutors office is gathering data to conduct its own criminal investigation into the allegations raised, which could lead to considerable fallout for the UPP.

Some party members and progressive supporters outside the party have been persistently calling for the resignation of the leadership that failed to control the candidate selection process in the primary.

They have also called for all six proportional representatives who have been elected to step down.

Such calls have been rejected by Lee and the East Gyeonggi Coalition as being biased. The main faction had rejected the resignation of proportional representatives.

The central committee meeting that opened earlier in the day was called to address all outstanding issues surrounding the incidents and iron out differences with the coalition party.

Besides the six lawmakers picked by party members, the UPP won seven seats in the election, making them the third-largest party in the 300-seat National Assembly after the ruling Saenuri Party and main opposition Democratic United Party.

Despite the results of the initial probes, there is disagreement within the party regarding the investigations. The largest faction has opposed a reshuffle of the party and rejected the idea of creating an interim emergency committee to resolve the current impasse.

Party watchers said there have been considerable under-the-table negotiations to end the standoff, yet due to the wide gap in how best to settle the issue, a compromise may not be forthcoming. (Yonhap)