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The Dow Jones Industrial Average was off 34.81 points (0.28 percent) to 12,560.94 in the first 15 minutes of trade.
The broader S&P 500 was down 2.79 (0.21 percent) to 1,334.98, while the tech-heavy Nasdaq Composite fell 9.51 (0.34 percent) to 2,818.96.
Earlier Asian and European stocks were also mostly down, with arrest of the man who spearheaded the International Monetary Fund's involvement in Europe's bailouts heightening worries about how Greece's debt crisis will be handled.