* Nations must stand up over Syria chemical weapons-Secretary of State
* Amgen, Onyx shares rise after announcing $10.4 billion deal
* Indexes: Dow falls 0.2 pct; S&P down 0.2 pct; Nasdaq up 0.1 pct
By Angela Moon
NEW YORK, Aug 26 (Reuters) - U.S. stocks turned negative on Monday after U.S. Secretary of State John Kerry said all nations must stand up for accountability on the use of chemical weapons in Syria.
Wall Street had been trading higher until Kerry's comment in midafternoon. Adding to the market's geopolitical nervousness, the White House said evidence of Syria's use of chemical weapons was undeniable.
Stocks rose for most of the session, as sharply weaker orders for long-lasting manufactured goods eased investors' worries of a cutback in economic stimulus.
"The turnaround (in stocks) is probably a reaction to the Secretary of State Kerry's comments. We are seeing signs of escalation here and geopolitical concerns are trumping," said Peter Cardillo, chief market economist at Rockwell Global Capital in New York.
The Dow Jones industrial average was down 53.84 points, or 0.36 percent, at 14,956.67. The Standard & Poor's 500 Index was down 6.38 points, or 0.38 percent, at 1,657.12. The Nasdaq Composite Index was down 2.98 points, or 0.08 percent, at 3,654.82.
Amgen Inc was the biggest boost to both the S&P 500 and Nasdaq 100 indexes after it struck a deal to buy cancer drug maker Onyx Pharmaceuticals Inc for about $10.4 billion, sweetening its original offer made in June.
Onyx shares rose 5.6 percent to $123.48 and Amgen jumped 8 percent to $113.93. The NYSEArca biotech index climbed 2.4 percent.
Earlier, data showed durable goods orders dropped 7.3 percent in July, the biggest decline in nearly a year. In addition, a gauge of planned business spending on capital goods tumbled, casting a shadow over the economy early in the third quarter.