WASHINGTON (REUTERS) - Wall Street looked set to open lower on Wednesday, weighed down by Apple after the world's most valuable company by market value reported a surprise fall in iPhone sales.

Shares of Apple dropped nearly 2 per cent to US$144.75 after the company also forecast current-quarter revenue below estimates. "The market is taking its cue from Apple," said JJ Kinahan, chief market strategist at TD Ameritrade in Chicago.

Strong corporate reports so far had resulted in estimates for first-quarter profit growth at S&P 500 companies increasing to 13.9 percent as of Tuesday, from an estimate of 10.4 per cent growth two weeks back, according to Thomson Reuters I/B/E/S.

The strong earnings have also helped offset some fears about geopolitical tensions in the Korean peninsula, the lack of progress by the Trump administration in enacting its economic agenda as well as mixed economic data.

"Strong earnings are still driving the market. Not only are earnings good, the CEOs are painting a picture of continued earnings growth and this helps trump some of the other factors,"said Kinahan.

At 9:39 a.m. ET (9:39 p.m Singapore time) the Dow Jones Industrial Average was down 40.41 points, or 0.19 per cent, at 20,909.48.

The S&P 500 was down 5.94 points, or 0.24 per cent, at 2,385.23 and the Nasdaq Composite was down 25.64 points, or 0.42 per cent, at 6,069.73.

Ten of the 11 major S&P 500 sectors were lower, with the technology index's 0.55 percent fall leading the decliners.