South Korea's parliamentary Speaker resigned on Thursday over a bribery scandal which has tarnished the conservative ruling party in a key election year.

Park Hee-Tae was alleged to have offered cash envelopes to lawmakers of the Grand National Party before a vote to select a new party chief in 2008.

He was elected to serve as party chief from 2008-2009 and became National Assembly speaker in 2010.

In a brief resignation statement read by his spokesman, Park said he was "really sorry" for the scandal but did not acknowledge personal wrongdoing.

"Please lay all responsibility on me... I intend to quit my position," his statement said.

The scandal was exposed by a GNP lawmaker who said he received a cash bribe from Park's aide which he returned. It prompted a major probe by prosecutors and dealt a blow to the conservatives, already suffering from waning support.

The party now holds 166 of the 299 parliamentary seats along with the presidency. But it anticipates a struggle in the April general election and the presidential poll in December amid a sharp slide in voter confidence.