The KOSPI slumps nearly 4 percent to the 6,500 level on large-scale net selling by foreigners and institutions. As concerns persist over rising international oil prices and market interest rates, heavyweight stocks such as Samsung Electronics and SK Hynix weaken in tandem, deepening the index's decline.

On Tuesday, the KOSPI ends down 273.08 points, or 3.99 percent, at 6,562.72. It opens down 210.33 points, or 3.08 percent, at 6,625.47. The index trims losses to as little as 6,694.57 during the session, but selling strengthens again in the afternoon, pushing it down to the 6,500 level.

In the main bourse, foreigners post net sales of 1.91 trillion won and institutions sell a net 2.04 trillion won. Combined net selling by foreigners and institutions totals 3.95 trillion won. Retail investors buy a net 2.30 trillion won, absorbing supply.

Most top market-cap stocks fall. Samsung Electronics closes down 4.02 percent at 250,500 won, while SK Hynix ends 4.73 percent lower at 1,613,000 won.

SK Square slumps 7.97 percent to 982,000 won. Hyundai Motor falls 5.62 percent to 378,000 won and LG Energy Solution closes down 5.31 percent at 347,500 won.

Samsung C&T falls 4.48 percent and Samsung Electro-Mechanics slips 2.10 percent. Samsung Biologics and KB Financial Group also decline 1.25 percent and 1.23 percent, respectively.

The KOSDAQ also falls. It ends down 17.27 points, or 2.10 percent, at 803.98. It barely holds above 800.

In Seoul's foreign exchange market, the won-dollar exchange rate is 7.00 won lower at 1,368.50 won.

The market is seen as extending losses as foreign and institutional selling continues amid pressure from rising international oil prices and market interest rates. Early bargain hunting briefly narrows the decline, but supply re-emerges in the afternoon, led by large-cap stocks.