South Korean shares fell for three straight days on Friday as concerns over Europe\'s debt crisis still weighed on investor sentiment despite positive job data in the United States, analysts said. The benchmark Korea Composite Stock Price Index (KOSPI) dropped 20.6 points, or 1.11 percent, to close at 1,843.14. Trading volume stood at 466.88 million shares worth 4.36 trillion won (3.75 billion U.S. dollars). The KOSPI stayed in the negative terrain throughout the session, continuing to extend its initial losses due to selling by foreign and institutional investors who feared the lingering European fiscal crisis. \"France\'s bond auction was not a disaster as some had feared, but worries about the possible credit rating downgrade of the country failed to calm investors,\" Yoo Kyung-ha, an analyst at Dongbu Securities in Seoul, told Xinhua. Yoo said that the KOSPI fluctuated sharply in the afternoon on rumors that light-water reactors exploded at the Yongbyon atomic complex of the People\'s Republic of Korea (DPRK), adding that the ungrounded rumors led to foreign selling on index futures, triggering program-linked selling on the spot. The country\'s financial regulator said that it would examine whether some speculators circulated the rumors in a bid to win profits from buying put options, whose holders gain profits when stock prices fall. Foreign investors were net sellers worth 53 billion won, and institutional investors sold a net 76.9 billion won worth of shares, snapping their five-day buying streak. Program-linked transaction shifted to net selling in four trading days, but retail investors limited further losses by purchasing a net 324.1 billion won worth of stocks. The positive U.S. job data helped avoid market sentiment\'s further worsening. The U.S. private sector employment climbed 325, 000 in December, stronger than expected, while initial jobless claims dropped by 15,000 last week, also beating the expectation. Attention was focused on the U.S. non-farm payroll report scheduled for Friday, analysts said. Market bellwether Samsung Electronics retreated 1.42 percent to 1,040,000 won as foreign investors moved to lock in recent profits despite the announcement of record earnings estimates. The preliminary Samsung operating profit was estimated at a fresh record high of 5.2 trillion won (4.5 billion dollars) in the fourth quarter of 2011. Cyclical shares largely lost ground. The world\'s No. 3 steelmaker by market cap POSCO fell 1.66 percent to 385,500 won, and the country\'s top automaker Hyundai Motor and its affiliate Kia Motors dropped around 2 percent. Crude oil refiners, which rallied recently amid higher oil prices, ended bearish as concerns over Europe and large stockpiles in the U.S. drove down global oil prices. Top crude refiner SK Innovation lost 0.65 percent to 153,500 won, and GS Holdings, parent company of the nation\'s No. 2 refiner, dipped 1.49 percent to 53,000 won. The local currency closed at 1,162.9 won against the greenback, down 10.2 won from Thursday\'s close. Bond prices ended lower. The yield on the liquid three-year treasury notes gained 0.01 percentage point to 3.35 percent, and the return on the benchmark five-year government bonds added 0.01 percentage point to 3.5 percent.