The focus was squarely on the end of the Federal Open Market Committee's two-day meeting and policymakers' take on whether the strength of the world's largest economy warrants an easing of stimulus.
The FOMC is scheduled to release a statement at 2pm in Washington, followed by Fed Chairman Ben Bernanke's news conference at 2.30pm.
Opinions are widely divided on whether policymakers will announce a start to easing their monthly bond-buying today.
"We expect tapering in the first quarter of next year," Jim Russell, senior equity strategist at US Bank Wealth Management, told Reuters. "Today's announcement will be whether they will signal that today or wait until Janet Yellen becomes Fed chief."
Yellen will succeed Bernanke when his term expires at the end of January.
In afternoon trading in New York, the Dow Jones Industrial Average gained 0.04 percent. Gains in shares of Exxon Mobil and Chevron outweighed declines in shares of Microsoft and Boeing, lifting the Dow.
The Standard & Poor's 500 Index fell 0.09 percent, while the Nasdaq Composite Index dropped 0.51 percent.
There were more signs of strength in the US economy. Housing starts soared 22.7 percent to a 1.09 million annualised rate, the highest since February 2008, according to Commerce Department data.
"The economy seems to be picking up and there's quite a lot of pent-up demand," David Sloan, a senior economist at 4Cast in New York, told Bloomberg News. "Even if the Fed does start to taper, I think the housing market will prove resilient."
Indeed, some said the Fed should begin easing its pace of bond-buying now.
"The last piece of the economic puzzle is falling into place and the expansion is assured. The last argument against tapering fell today, let's hope the Fed hears the news," Chris Rupkey chief financial economist at Bank of Tokyo-Mitsubishi UFJ in New York, told Reuters.
Meanwhile shares of FedEx, considered an economic bellwether, were flat at US$139.05 after the company posted net income that fell short of analysts' estimates, even as it lifted the range of its full-year earnings forecast.
FedEx is "on track to be where we need to be by the end of 2016," FedEx Chief Financial Officer Alan Graf said on a conference call with analysts and investors, Bloomberg reported. "We are managing very aggressively the tradedown in international."
In Europe, the Stoxx 600 Index finished the session with a 0.9 percent increase from the previous close. The UK's FTSE 100 eked out a 0.1 percent gain, while France's CAC 40 climbed 1 percent and Germany's DAX added 1.1 percent.