Seoul shares opened slightly higher Wednesday as a widespread investigation into President Yoon Suk Yeol's brief martial law declaration by various law enforcement agencies gained traction.

The benchmark Korea Composite Stock Price Index added 6.44 points, or 0.27 percent, to 2,424.28 in the first 15 minutes of trading.

The president faces a criminal investigation in connection with insurrection and other charges related to his short-lived martial law order last week.

Earlier in the day, heads of the National Police Agency and the Seoul Metropolitan Police Agency were placed under emergency arrest in connection with their alleged involvement.

Overnight, the US stock market declined amid concerns in the semiconductor industry following the earnings report from TSMC, the world's largest foundry, and caution ahead of the release of inflation data

The tech-heavy Nasdaq composite dropped 0.25 percent, and the S&P fell 0.3 percent. The Dow Jones Industrial Average edged down 0.35 percent.

In Seoul, battery and energy shares advanced, with LG Energy Solution up 0.39 percent and SK Innovation adding 0.59 percent.

Steel and financial shares also gained ground, with top steelmaker Posco Holdings rising 0.37 percent and Shinhan Financial gaining 1.1 percent.

Leading air carrier Korean Air rose 1.27 percent as it was set to finalize its protracted merger deal with industry rival Asiana Airlines later in the day.

The local currency was trading at 1,433.60 won against the greenback at 9:15 a.m., down 6.70 won from the previous session. (Yonhap)