* Market sells off in afternoon after Ukraine-related headlines
* Treasury yields fall, gold ticks higher
* Indexes off: Dow 1.0 pct, S&P 1.1 pct, Nasdaq 0.9 pct (Updates prices, comment)
By Rodrigo Campos
NEW YORK, Aug 5 U.S. stocks fell on Tuesday in broad selling led by energy shares as crude prices fell and as traders cited concern about possible escalation of military action in eastern Ukraine.
Selling accelerated in the afternoon after a Bloomberg report that cited the Polish Foreign Minister and said Russian units were poised to pressure or invade Ukraine.
"The market was vulnerable to begin with, with a number of commentators questioning Monday's rebound," said Quincy Krosby, market strategist at Prudential Financial in Newark, New Jersey.
She cited the concerns over Ukraine, saying "volume is very light and the market can be skewed in any direction with a headline crossing the wires."
Spot gold prices turned higher after trading down for most of the session. Benchmark U.S. Treasury yields hit session lows.
The market was pressured throughout the session by weak earnings, including from Target and Cablevision. Figures showing China's services purchasing managers' index fell to 50.0 in July, the lowest since data collection began in November 2005, also weighed.
Energy stocks posted the largest losses on the S&P 500, down 2.5 percent with crude oil prices down as increasing supply overshadowed political tensions and on pressure from the Chinese data. The S&P energy index has fallen in seven of the last eight sessions.
Pioneer Natural Resources ranked among the top S&P 500 decliners with a 5.7 percent slide to $209.79 after the oil and gas exploration and production company's revenue missed estimates.
The Dow Jones industrial average fell 170.6 points or 1.03 percent, to 16,398.68, the S&P 500 lost 21.62 points or 1.12 percent, to 1,917.37 and the Nasdaq Composite dropped 41.22 points or 0.94 percent, to 4,342.67.
Retailer Target cut its second-quarter earnings estimate due to higher promotions and discounts and its shares fell 4.2 percent to $58.16.
Cablevision fell 7 percent to $18.08 as subscriber losses doubled in the second quarter from the previous quarter as it cut down on promotions.
Shares of solar and LED equipment maker GT Advanced Technologies rose 5.8 percent to $14.95 a day after it raised the lower end of its full-year 2014 adjusted profit forecast, citing higher gross margins.
The market had gotten support from data showing new orders for U.S. factory goods rose more than expected in June as demand increased across the board, while a measure of growth in the services sector increased at the fastest rate in 8-1/2 years, drawing a healthy picture for the world's largest economy. (Reporting by Rodrigo Campos; additional reporting by Chuck Mikolajczak; Editing by Bernadette Baum and Nick Zieminski)