The won ended December down 5.2 per cent against the dollar, marking its largest monthly decline in 22 months, after reaching its weakest level since March 2009 due to domestic political turmoil.

Last month, South Korea's consumer inflation quickened to 1.9 per cent, exceeding market expectations and near the BoK's 2 per cent target, with the central bank flagging a possibility of inflation accelerating further this month.

The BoK is expected to lower interest rates by a quarter percentage point to 2.75 per cent on Thursday, a month earlier than previously anticipated, to support a struggling economy amid risks from political uncertainty.