Before the announcement at 1800 GMT, markets tended to expect no change for at least another month. But the uncertainty left Europe's main share markets at a virtual standstill after two days of gains.
Rises overnight in Asia meant MSCI's all-world share index had managed a three-week high, but it was small scale. Currency and bond market moves were low key, too.
The dollar was under some pressure, mostly from the euro. Weak U.S. inflation data had underscored one of the arguments for the Fed to hold fire. Wall Street was set f or a subdued start and oil and other commodities gave back some of their recent gains.
"I think path (timeline for future moves) is more important than the rate decision today," said Didier Duret, Chief Investment Officer at ABN Amro.
"They want to stabilise the market's confidence, so I think they will wait till October ... but they will maintain a very prudent and cautious approach, after all they are still the masters of the universe."
When it comes, the U.S. central bank's move will be the first rise in its interest rates since 2006. It will lift rates from near zero, where they have been since the depths of the global financial crisis in late 2008.
Markets had expected the Fed to raise rates for most of this year, but those expectations have faded following a bout of global market turmoil over the last couple of months, especially in China.
Futures pricing suggests an only one change in four that it will pull the trigger. The latest poll by Reuters on Wednesday also showed the majority of economists now expect no hike, although it remains a close call.
FEDY STEADY? GO?
Wall Street's S&P 500, Dow Jones Industrial and the Nasdaq indexes were expected to spend the final hours of the Fed countdown in the red after all three hit near one-month highs on Wednesday.
MSCI's 45-country all world index had reached a similar peak overnight after Japan's Nikkei shrugged off another drop in exports to climb 1.4 percent and Australian and Malaysian shares rose 1 and 1.8 percent.
There was a late 2 percent dip in Chinese stocks, but after their recent volatility it raised few eyebrows.
Even if the Fed were to raise rates later, many market players expect officials to signal a cautious stance on the pace of future increases, rather than herald a brisk series of increases.
There is also the comfort that both the European Central Bank and the Bank of Japan appear to be gearing up for fresh rounds of stimulus and rates are still being cut in many parts of the world.
Switzerland's central bank said on Thursday, for example, that its negative interest rates, the lowest in the world, would stay in place for the foreseeable future, as it seeks to weaken a "significantly overvalued" Swiss franc and combat a deeper-than-expected bout of deflation.
The latter worry was pinned on the recent slump in oil prices.
They appear to have largely stabilised over the last month following their April to August swoon but were giving up ground again ahead of U.S. trading. US West Texas Intermediate (WTI) crude was down 1.5 percent at $46.45 per barrel and Brent back under $50 a barrel to $48.90.
Gold, also dipped to $1,120 per ounce and silver and other metals markets were down too after most had made decent gains on Wednesday.
In bond markets there was no getting away from the Fed debate. The yield on the U.S. two-year treasury note, seen as most sensitive to the Fed's decision, held near a 4 1/2-year high at 0.803 percent.
Even if the central bank doesn't pull the trigger later, it is still expected to by the end of the year.
Euro zone bonds were largely steady, meanwhile, as France and Spain breezed through the potentially uncomfortable task of selling debt hours before the U.S. rate decision.
(Additional reporting by Marius Zaharia in London and Saikat Chatterjee in Hong Kong)
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