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The local currency rose 0.5 percent to stand at 1,123.0 per dollar at 0025 GMT, compared to Thursday's local close at 1,128.4. It opened at an intraday high of 1,122.0, the won's highest level against the dollar since April 3 this year.
Seoul shares shot up more than 2 percent after the US central bank announced it will buy $40 billion of mortgage-backed debt per month until job rates in the country improve.
Fed Chairman Ben Bernanke also said it would keep overnight interest rates at their current near-zero level until at least mid-2015.
Local bond prices fell, with September futures on three-year treasury bonds falling 0.14 points to trade at 105.79.