South Korean-related assets slumped after the country's president declared martial law, raising investor concerns about political instability and unrest. The iShares MSCI Korea ETF fell 5.1 percent in U.S. markets, its biggest one-day drop since Aug. 5. The won fell to its lowest level against the dollar in more than two years. Shares of London-listed Samsung Electronics fell 5 percent. Uncertainty within South Korea has increased under external pressure in recent weeks as markets have begun to digest the possibility of higher U.S. tariffs under the new Trump administration, said Arup Chatterjee, a strategist at Wells Fargo in New York. Other South Korean companies, ADRs, also fell. Coupang Inc. fell 6.9 percent in U.S. stocks, while Posco Holdings Inc. and KB Financial Group Inc. also fell.