US STOCKS-NYSE imposes trading curbs as stocks tumble

(Updates with trading curbs)

NEW YORK, July 26 (Reuters) - The New York Stock Exchange said on Tuesday it instituted downside trading curbs at 11:06 a.m. (1506 GMT) as U.S. stocks fell sharply on concerns about deterioration in the credit markets.

The New York Stock Exchange Composite Index , which is used to determine when to begin trading curbs, was down 205.45 points, or 2.07 percent, at 9,724.47.

The trading curbs require that all program selling of S&P 500 stocks must be on an up-tick.