Analysts attributed the drop to the escalating concern that the North will soon press ahead with another nuclear test and a long-range missile launch.

Concerns over a potential clash with North Korea have been fueled by the Donald Trump administration's recent air strike against Syria.

"The influence of the geopolitical crisis of the Korean Peninsula may continue for the time being," said Lee Kyung-min, a researcher at Daishin Securities Co.

Foreigners offloaded a net 127.7 billion won, while individual investors scooped up a net 31.6 billion won. Institutions bought a net 97.7 billion won.

Tech shares closed mixed, with Samsung Electronics falling 0.81 percent to 2,080,000 won and SK hynix losing 0.31 percent at 48,850 won. LG Display advanced 2.49 percent at 30,850 won on the market rumor that Google may invest 1 trillion won on its OLED production line.

Carmakers lost ground, with Hyundai Motor falling 2.4 percent to 142,500 won and Kia Motors falling 1.55 percent to 35,000 won.

Auto parts maker Hyundai Mobis shed 1.58 percent to 218,500 won.

Steelmakers also closed lower, with No. 1 POSCO falling 0.37 percent to 271,500 won and Korea Zinc sliding 0.12 percent to 409,500 won. Hyundai Steel moved down 0.35 percent to 56,200 won.

The local currency closed at 1,145.80 won against the US dollar, down 3.6 won from the previous session's close.

Bond prices, which move inversely to yields, closed higher. The yield on three-year Treasurys fell 2.9 basis points to 1.693 percent, and the return on the benchmark five-year government bond shed 3.9 basis points to 1.887 percent. (Yonhap)