The benchmark 5-year treasury bond yield ended unchanged at 4.28 percent while the 10-year yield added 1 basis point to 4.68 percent. March-delivery futures on 3-year treasury bonds fell 0.04 point to 102.96.

"The turmoil in Libya will make it difficult (for the central bank) to raise interest rates despite concerns about inflation," said a bond dealer at a domestic securities company.

"The monetary policy committee has tended to be more sensitive to external factors than domestic ones," he said, referring to the policy-making board of the Bank of Korea.

Data released before markets opened on Wednesday showed South Korea's annual inflation in February quickened more than expected to a 27-month high of 4.5 percent, also far above the 4 percent ceiling of the central bank's target band. The data in principle increases the chances for monetary policy tightening but investors bet the Bank of Korea, which has repeatedly wrong-footed market expectations, would possibly pay more attention to the political unrest in the Middle East.

Foreign investors were in fact net buyers of more than 4,000 contracts in the 3-year treasury futures trading.

The won also finished the domestic session almost unchanged, while Seoul shares fell more than half a percent.