Stocks accelerated their selloff in the final hour of trading Friday to close at session lows, logging their worst weekly decline for the year, as ongoing signs of weakness overseas and tepid economic news in the U.S. kept investors on edge.

The Dow Jones Industrial Average tumbled 136.99 points, or 1.05 percent, to close at 12,849.59, led by BofA and JPMorgan .

The S&P 500 slumped 17.31 points, or 1.25 percent, to finish at 1,370.26, a closely-watched technical level. The Nasdaq declined 44.22 points, or 1.45 percent, to end at 3,011.33.

The CBOE Volatility Index, widely considered the best gauge of fear in the market, soared to finish above 19.

For the week, the Dow fell 1.61 percent, the S&P dropped 1.99 percent, and the Nasdaq plunged 2.25 percent. Among the Dow components, BofA was the biggest weekly laggard, while H-P climbed.

All 10 S&P sectors ended in the red for the week, led by financials and energy. Techs posted their first weekly loss for the year.

CSTR News & Analysis

 Tough Times for Short Sellers in This Bull Market - 14 May 2013 EDT - CNBC.COM

 MARKET PULSE-Pfizer, Freescale, LogMeIn, Expedia, Tyco, Amazon - 26 Apr 2013 EDT

 MARKET PULSE-Boeing, Tyco, LDK Solar, Amazon, Starbucks - 26 Apr 2013 EDT

 MARKET PULSE-Boeing, Avanair, LDK Solar, Amazon, Starbucks - 26 Apr 2013 EDT

 MARKET PULSE-Pfizer, Apple, Pulte, Synaptics, Perkinelmer - 26 Apr 2013 EDT

 More CSTR News