Dow Jones plunges more than 260 points amid massive market sell-off by Tom Huddleston, Jr. @FortuneMagazine September 25, 2014, 4:57 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons A volatile week for U.S. markets took a turn for the worse on Thursday when stocks tumbled amid investor concern about global instability and the possibility of higher interest rates. The Dow Jones Industrial Average fell 264 points, or 1.5%, to close below the 17,000-point mark at 16,945.80. All 30 companies on the blue-chip index saw their shares drop. JPMorgan Chase JPM and UnitedHealth Group UNH saw the biggest declines among Dow Jones companies, dropping 2.4% and 2.3%, respectively. The S&P 500 and the Nasdaq fell 1.6% and 1.9%, respectively, as each index has now declined in four of the past five days of trading. Tech stocks led the broader decline and Apple AAPL was one of worst performers on what was one of the market’s poorest days of the year. Apple fell 3.8% after the tech giant was forced to pull an update to its new iOS8 because some users complained the update caused their phones to lose the ability to make calls. Yahoo YHOO was also down Thursday, falling 2.3%, while both Google GOOG and Microsoft MSFT fell 2.3%. Alibaba BABA fell 1.8% and is down 4.9% for the week after a record-setting market debut saw the Chinese e-commerce giant’s shares up by 38% last Friday on its first day of trading. Markets had fallen off on both Monday and Tuesday of this week before experiencing a rebound on Wednesday. The airstrikes in Syria had pushed stocks down earlier in the week, as did the Obama administration’s newly-announced regulations aimed at fighting corporate tax inversions. As it stands, the Dow Jones is down 1.9% for the week and the S&P 500 is off by 2.2% while the tech-heavy Nasdaq is down by 2.5%. Richard Fisher, president of the Federal Reserve Bank of Dallas, said on Thursday that the U.S. Federal Reserve could start raising interest rates in the spring of 2015, which is slightly earlier than had previously been indicated. Meanwhile, markets continued to react to the U.S.-led airstrikes in Syria, while a report that there might be a leadership change at China’s central bank also created uncertainty among investors. The Chicago Board Options Exchange Volatility Index (VIX), commonly known as the “fear index,” jumped 17.9% on the day.