US stocks have plunged as the country moves closer to punitive military action against Syria for its alleged use of chemical weapons in a devastating attack on civilians.

Warnings stepped up from the United States, France and Britain that Damascus would be held accountable for the August 21 attack, sparking market worries of a possible broader conflict.

At the closing bell on Tuesday, the Dow Jones Industrial Average was down 170.56 points (1.14 per cent) at 14,775.90.

The broader S&P 500 index fell 26.30 (1.59 per cent) to 1,630.48, while the tech-heavy Nasdaq Composite lost 79.05 (2.16 per cent) at 3,578.52.