Dow Jones industrials and Standard & Poor's 500 index has fallen to levels not seen in nearly four months.
Analysts said trading was uneven as investors made short-term bets on whether or when the US would wage war on Iraq. Tensions with North Korea also pressured the market.
The Dow fell 55.88, or 0.7% to close at 7,929.30, for a three-day loss of 180 points. It was the lowest level seen since October 14, when blue chip stocks finished at 7,877.40.
The broader market finished mixed. The S&P 500 index dropped 5.44, or 0.6%, to 838.15, the lowest since October 11, when it closed at 835.32. The Nasdaq composite index inched up 0.23, or 0.02%, to 1,301.73.