U.S. stocks opened lower on Tuesday, putting the S&P on pace for a third straight fall, as conflict in the Middle East intensified and after the U.S. Treasury moved to curb "tax inversion" deals.

The Dow Jones industrial average .DJI fell 41.16 points, or 0.24 percent, to 17,131.52, the S&P 500 .SPX lost 5.29 points, or 0.27 percent, to 1,989 and the Nasdaq Composite .IXIC dropped 11.91 points, or 0.26 percent, to 4,515.78.