Offshore investors were poised to snap an 11-day buying spree, selling a net 29.3 billion won ($26.2 million) worth of South Korean shares.

"Policies from Europe and the US exceeded expectations but the mismatch between hopes and actual execution have limited the stock market rally," said Oh Seung-hoon, a strategist at Daishin Securities in Seoul.

Oh said domestic stocks could rise if global oil prices are to stabilise and Spain reaches out for external aid to clean up its balance sheet.

The Korea Composite Stock Price Index (KOSPI) was down 1 percent at 1,981.82 points in morning trade

It has slipped 1.1 percent from a five-month high marked on Sept. 14 when the Federal Reserve unveiled a third round of quantitative easing but remains 12.5 percent higher than this year's lowest level marked in late July.

Stocks lost ground across the board with securities and banking stocks leading declines.

Hyundai Securities fell the most among its peers, down 3 percent. Hana Financial Group slid 3.9 percent to post the biggest loss among financials.

"Securities stocks recently saw daily gains that outperformed the bourse by nearly 200 percent, and banks are usually the first to go when offshore investors start selling," said Baek Woon, an analyst at IM Investment and Securities in Seoul.

Tech bellwether Samsung Electronics was down 0.2 percent after its biggest competitor Apple Inc released its latest smartphone, the iPhone 5, on Sept. 21. South Korea's second-largest smartphone manufacturer LG Electronics fell 2 percent.

Decliners far outnumbered gainers 513 to 285.

The KOSPI 200 benchmark of core stocks was down 0.8 percent while the junior KOSDAQ was up 0.1 percent.