South Korean financial markets opened sharply lower on Thursday, pressured by attacks on key Middle Eastern energy facilities and the U.S. Federal Reserve's decision to hold interest rates steady. The South Korean won also weakened significantly against the U.S. dollar, breaching the 1,500 won threshold.

The Korea Composite Stock Price Index (KOSPI) dropped 128.08 points, or 2.16 percent, to 5,796.95 in the first 15 minutes of trading.

Overnight, U.S. stock indices declined, with the Dow Jones Industrial Average falling 1.63 percent, the Nasdaq Composite dropping 1.46 percent, and the S&P 500 decreasing 1.36 percent.

An Israeli strike on Iran's largest South Pars gas field prompted retaliatory attacks by Iran on a major liquefied natural gas facility in Qatar. These events dampened investor risk appetite and pushed global oil prices higher again.

The U.S. Federal Reserve's choice to maintain its policy rate in the 3.5-3.75 percent range also contributed to the weaker market sentiment.

In Seoul, most large-cap stocks opened lower.

Market leader Samsung Electronics fell 2.64 percent, while its chipmaking rival SK Hynix declined 2.84 percent.

Automotive giant Hyundai Motor dropped 3.12 percent, and its affiliate Kia decreased 1.71 percent.

AI-focused investment firm SK Square slid 2.22 percent, and leading battery maker LG Energy Solution was down 1.96 percent.

Major defense company Hanwha Aerospace fell 1.33 percent, and leading shipbuilder HD Hyundai Heavy Industries dropped 2.37 percent.

Biotech firm Celltrion declined 3.1 percent.

As of 9:15 a.m. local time, the won was trading at 1,500.4 per U.S. dollar, down 17.3 won from the previous session.