The benchmark KOSPI slipped more than 2% to around 6,920 on Friday, snapping a three-day rally as escalating tensions in the Middle East dampened investor sentiment.
Brent crude climbed above $100 per barrel after reported attacks on Saudi oil tankers, while US President Donald Trump said he was considering a "massive attack" on Iran, heightening fears of further disruptions to global oil supplies and prompting a broad risk-off move across global markets.
The market also came under pressure from a selloff in technology stocks following disappointing earnings from major US companies, weighing on South Korean chipmakers.
Separately, fresh US tariffs of up to 12.5% on South Korea and other trading partners over forced labor concerns added to uncertainty over the export outlook.
Among heavyweights, Samsung Electronics (-3.6%), SK hynix (-3.1%), SK Square (-6.1%), Hyundai Motor (-6.1%), LG Energy Solution (-3.7%), and KB Financial Group (-5.0%) all declined.