The local currency was quoted at 1,084.1 against the dollar at the end of onshore trade, compared with 1,086.5 at the end of the Seoul session on Wednesday.

US House of Representatives Speaker John Boehner voiced optimism that the Republican Party can strike a deal with President Barack Obama to avoid crippling tax hikes and spending cuts from taking effect next year.

But dealers said the won's gains were capped, with a relatively small amount of dollars being sold by exporters. Some dealers also suspected that the local foreign exchange authorities had intervened to slow the currency's rise.

"The won has failed to rise above 1,084 against the dollar throughout this week, so it would be strange for the authorities to suddenly concede this level," a local bank dealer said.

The benchmark Korea Composite Stock Price Index ended up 1.2 percent at 1,934.85. Foreigners were net buyers of 45.9 billion won ($42.25 million) worth of local shares on Thursday.

Local bonds were nearly flat, with investors remaining cautious about the global economic outlook. December futures on three-year treasury bonds ended down 0.01 points at 106.08.

Yields on the benchmark five-year treasury bonds and the three-year treasury bonds were unchanged from Wednesday.