United States stocks have closed sharply lower after Secretary of State John Kerry warned that the US would demand "accountability" after an "obscene" chemical weapons attack on Syrian civilians.
The Dow Jones Industrial Average shed 63.97 points (0.43%) at 14,946.54.
The broad-market Standard & Poor's 500 index fell 6.71 (0.40%) to 1,656.79 and the tech-rich Nasdaq Composite slipped 0.22 (0.01%) to 3,657.57.
The markets ended firmly in the red in choppy trade on Monday after trading solidly higher for most of the day.
The sell-off came immediately after Kerry said the US was still examining evidence of the use of chemical weapons in Syria but left no doubt that Bashar al-Assad's regime would be blamed.
The top US diplomat said President Barack Obama would demand accountability for this "moral obscenity".
During the session data showed orders for long-lasting manufactured goods dropped sharply in July as demand for aircraft fell and business spending was weak.