The chairman of South Korea's ruling Uri party has quit following its heavy defeat in local and regional elections.
Mr Chung said he "failed to keep his promise"
Chung Dong-young said he was taking all responsibility for the results, which saw Uri win just one of 16 key regional posts at stake.
The main opposition Grand National Party (GNP) took 12 twelve posts, including the capital, Seoul.
The poll could have far reaching consequences for the South's ties with North Korea, correspondents say.
"I failed to keep my promise," Mr Chung was quoted as saying by Uri party officials.
"The responsibility for the election defeat lies on the party chairman," he added.
The GNP secured 12 key posts in Wednesday's elections, the electoral commission said.
The smaller Millennium Democratic Party won two races and one post went to an independent candidate.
The results of the poll are not surprising as Uri had openly predicted disaster, saying it had failed to read the minds of the people, correspondents say.
The GNP has also gained public sympathy as a result of a knife attack by an unemployed ex-prisoner on party leader Park Geun-hye during election campaigning 10 days ago.
She suffered an 11cm (four inch) cut to her cheek which required 60 stitches.
Roh under fire
The vote was also seen as a key test for the government of President Roh Moo-hyun, increasingly unpopular as it approaches its final year in office.
Mr Roh's government is accused by its opponents of being incompetent and divisive in its running of the economy and in foreign affairs.
The government has irritated the US with what is seen as an indulgent policy towards North Korea, despite the North's claim to be developing nuclear weapons.
A big win for the opposition strengthens its position in the run-up to presidential elections next year.
It may also boost the chances of Ms Park, daughter of former military President Park Chung-hee, of winning the presidency.
President Roh is prevented by law from seeking re-election.
The GNP has been pushing for a tougher line on aid to the North and for improved relations with the US.
North Korea has warned about a rise in what it sees as hostile political forces in the South.