Stocks fell at the open on Monday as worries about the euro-zone debt crisis increased after Standard & Poor's cut Italy's rating outlook and Spain's ruling Socialists suffered a setback in elections.

The Dow Jones industrial average <.DJI> was down 156.66 points, or 1.25 percent, at 12,355.38. The Standard & Poor's 500 Index <.SPX> was down 18.03 points, or 1.35 percent, at 1,315.24. The Nasdaq Composite Index <.IXIC> was down 48.07 points, or 1.71 percent, at 2,755.25.

(Reporting by Angela Moon, Editing by Kenneth Barry)