Three top officials of South Korea's ruling Grand National Party resigned Wednesday, raising turmoil in the organisation to crisis levels ahead of crucial elections next year.

The trio, members of the conservative GNP's seven-strong Supreme Council, said they were stepping down over a lack of reforms despite the party's plunging popularity ahead of presidential and parliamentary polls.

One of them called for the party to be disbanded and reformed under a new name after a top GNP lawmaker's assistant was arrested on charges of mounting a cyber attack on the country's election commission during a key vote last month.

Won Hee-Ryong said the hacking "undermined the basic principles of democracy" and was "worse" than past cyber attacks by North Korea.

Another of the three to resign, Yoo Seong-Min, told journalists: "I'm quitting the party post, taking responsibility for failing to rescue the party from a crisis of life or death."

He offered a public apology for what he called "people's despair and anger" toward his party.

Last month the GNP finally ratified a controversial free trade pact with the United States after years of delays, while relations with nuclear-armed neighbour North Korea remain tense.

Ruling party lawmaker Shin Ji-Ho said on YTN television that many voters see the GNP merely as a coterie of profiteers pursuing partisan interests at a time of global economic crisis.

The alleged cyber attack on the National Election Commission took place as a by-election for the Seoul mayoralty was being held in October.

The commission's homepage -- where voters could cast their ballots remotely -- was paralysed for two hours during the morning commute, sparking allegations it may have been a deliberate attempt to influence the election outcome.

Working age voters tend to favour opposition candidates in South Korea and reducing the number of votes polled by company employees was considered beneficial to the conservative ruling party.

In the event civic activist Park Won-Soon, backed by opposition parties, beat the GNP candidate by a large margin, in a major blow to the political establishment.

An assistant to the GNP's lawmaker in charge of publicity was arrested last week in connection with the incident.

GNP chairman Hong Jun-Pyo said Wednesday plans were being prepared to reform the party before April's parliamentary polls and a presidential vote in December 2012.