Wall Street edged lower on Wednesday after two Federal Reserve officials hinted at an interest rate hike as soon as this month.
Kansas City Fed President and voting member Esther George said the U.S. labour market could already be at full strength, one of the key conditions set by the Fed for considering an interest rate hike.
Richmond Fed President Jeffrey Lacker said the case for a rate hike in September was strong.
The Fed releases its Beige Book, a summary of commentary on economic conditions, at 2:00 p.m. ET (1800 GMT).
US stocks have been trading in a tight range in the past few months, with the S&P 500 not moving more than 1 per cent in either direction on a daily basis since July 8.
Investors will wait until they get more clarity on presidential elections, the quality of third-quarter earnings and the timing of the next rate hike, Courtney said.
At 12:33 p.m. (1633 GMT), the Dow Jones Industrial Average was down 57.15 points, or 0.31 per cent, at 18,480.97.
The S&P 500 was down 6.65 points, or 0.3 per cent, at 2,179.83.
The Nasdaq Composite was down 12.45 points, or 0.24 per cent, at 5,263.46, after touching an intraday high.
Nine of the 10 major S&P 500 indexes were lower, with the consumer staples index falling the most in six weeks.
Whole Foods fell 5.4 per cent and weighed the most on the index after smaller rival Sprouts Farmers Market painted a bleak picture for grocers with a disappointing quarterly outlook.
Apple shares were down 0.12 per cent at $107.62, after the biggest company by market value launched the new iPhone.