An employee sorts U.S. dollar banknotes at Hana Bank's counterfeit response center in central Seoul, Thursday. South Korea's foreign exchange reserves declined in May as authorities tapped reserves to help stabilize the won, which has come under pressure amid a sharp rise in the dollar. According to the Bank of Korea, the country's foreign reserves stood at $426.99 billion at the end of May, down $880 million from a month earlier. Yonhap

The Korean won weakened beyond the 1,560-per-dollar mark in overnight trading Friday and early Saturday, falling to its lowest level in 17 years as a stronger dollar and continued foreign selling weighed on the currency.

The won rose as high as 1,561.5 per dollar in overnight trading before closing at 1,559.0, according to Seoul foreign exchange market data. The move marked the weakest level for the won since March 2009 during the global financial crisis.

The currency had already weakened to 1,549.1 per dollar during regular trading Friday before ending the daytime session at 1,539.1. It then accelerated sharply after the release of stronger-than-expected U.S. employment data, breaking through the psychologically significant 1,550 and 1,560 levels in succession.