While economic data point to a recovery in the economy and strengthening labour market conditions, a crisis in Greece, turmoil in Chinese markets and a sharp selloff in commodities have all clouded the outlook for a near-term rate hike, analysts say.
"I think it's the most likely date right now," Jonathan Golub, chief U.S. market strategist at RBC Capital Markets told CNBC's "Squawk Box Europe," referring to the prospect of a rate hike at the Fed's September meeting.
"The odds among Wall Street folk are a little better than 50-50 but as an equity strategist, if they (the Fed) don't move in September, the market will take that as bad news," Golub said. "If you can't get to 25 basis points on the cost of short-term money what does that say to an equity investor who's trying to make a decision on whether to put risk capital out there?"
U.S. stocks closed about 1 percent higher on Tuesday as investors found encouragement from some recovery in oil prices and Chinese stocks, amid mixed earnings and the start of the Fed's two-day meeting.
Chinese stocks, which succumbed to heavy selling at the start of the week, rallied on Wednesday as investors took comfort from Beijing's efforts to stabilize a volatile stock market.
The benchmark Shanghai Composite stock index closed almost 3.5 percent higher – helping boost sentiment across global share markets. Most Asian stock markets ended the session higher, while European stocks rallied initially before trimming gains to trade mixed.
Read MoreChina trades warily as focus switches to the Fed
U.S. stock futures, meanwhile, were modestly higher with index futures for the blue-chip Dow Jones industrial average trading about 40 points higher.