South Korean stocks closed almost flat on Thursday as upbeat economic data offset concerns over instability in Syria and so-called quadruple witching, analysts said.

The benchmark Korea Composite Stock Price Index (KOSPI) added

0.21 points, or 0.01 percent, to finish at 2,004.06. Trading volume was moderate at 353.2 million shares worth 6.49 trillion won (US$5.99 billion) with gainers outstripping decliners 412 to 399.

"Quadruple witching erased the KOSPI's earlier gains as the selloff took place toward the closing bell. But there's no concern about direction of the market. We are seeing a solid and strong foreign inflow, which will likely continue for a while," said Han Beom-ho, an analyst at Shinhan Investment Corp.

"Quadruple witching" refers to the simultaneous expiration of contracts for stock index futures, stock index options, stock options and stock futures, and usually causes a volatile trading on the market.

It comes on every second Thursday of the month in March, June, September and December for Korea.

Foreigners snapped up a net 639.1 billion won worth of local equities, while retail and institutional investors dumped a net 355.8 billion won and 256.6 billion won, respectively.

Domestic-focused companies drove up the shares. Top mobile carrier SK Telecom jumped 3.98 percent to 222,000 won, and Naver, the No. 1 Internet portal operator, gained 2.54 percent to 525,000 won.

Market bellwether Samsung Electronics rose 0.57 percent to 1,410,000 won.

In contrast, steelmakers and automobile companies lost ground.

POSCO retreated 2.5 percent to 331,500 won, with Kia Motors falling 2.33 percent to 67,000 won.

Tradings of LG Chem, a leading chemical maker, and more than 150 other listed stocks including derivative instruments like exchange-traded funds were abruptly delayed for nearly an hour shortly after the opening bell due to a system malfunction at the Korea Exchange (KRX).

The local currency ended at 1,085.00 won against the greenback, up 1.5 won from Wednesday's close, largely due to a weaker dollar, dealers said. (Yonhap news)