South Korean stocks started almost flat Wednesday as investors remained cautious awaiting the US Federal Reserve's rate decision.

The benchmark Korea Composite Stock Price Index lost 1.61 points, or 0.06 percent, to 2,557.60 in the first 15 minutes of trading.

All three US stock indexes closed lower Tuesday on the eve of the Federal Reserve's interest rate announcement, which is expected to keep rates on hold.

But the market expects the US central bank may deliver one more rate hike this year as higher energy costs may heat up inflation and curb economic growth.

In Seoul, big-cap stocks traded mixed.

Samsung Electronics, the No. 1 memory chipmaker in the world, gained 0.14 percent, while its rival SK hynix lost 0.34 percent.

Steel giant Posco Holdings dipped 0.17 percent, but its chemical materials unit Posco Future M climbed 1.64 percent and its energy trading unit Posco International jumped 2.27 percent.

Battery shares started in positive terrain, with LG Energy Solution and Samsung SDI rising 0.3 percent and 0.18 percent, respectively.

Automakers got off to a strong start.

Top carmaker Hyundai Motor and its auto parts-making affiliate Hyundai Mobis both advanced 1.05 percent, and Kia added 0.5 percent.

Bio shares were weak, with Samsung Biologics dropping 0.82 percent and Celltrion retreating 0.27 percent.

The local currency was trading at 1,327.80 won against the US dollar at 9:15 a.m., down 0.7 won from Tuesday's close. (Yonhap)