[SEOUL] Seoul shares erased early gains to close flat on Thursday after a volatile session, as investors waited to see whether the US Federal Reserve would raise interest rates later in the day.

The Korea Composite Stock Price Index (KOSPI) closed at 1,976.49 points, barely changed from the previous close at 1,975.45 points. It climbed as high as 1,989.07 points at the opening, the highest intraday level since Aug 17.

Foreigners were net buyers for a second day, purchasing a net 131.1 billion won (S$157 million) of shares in the main board. They ended a 29-consecutive-session selling streak on Wednesday.

Samsung Heavy Industries Co Ltd and Samsung Engineering Co Ltd closed down 1.9 per cent and 8 per cent, respectively, after saying late in the session they had no plans to merge with each other.

Meanwhile, the South Korean won ended local trade up 0.9 per cent at 1,165.9 per dollar on offshore selling in the greenback ahead of the Fed's rate decision. It rose as high as 1,164.6 in late trading, the strongest since Aug 11.

REUTERS