Investors are waiting for the outcome later of the Federal Reserve's policy meeting, which will indicate how the central bank views the US economy.
Financial markets have priced in possible stimulus measures. However, economists are split over whether the bank will take action now.
One Fed option is to start buying up Treasury securities again - an action last taken during the financial crisis.
In July, Fed boss Ben Bernanke said the outlook was "unusually uncertain".
'QE lite'The dollar rose on Tuesday and world stocks slipped as investors remained cautious ahead of the meeting.
The Fed may choose to revive the "quantitative easing" (QE) scheme, pumping in more money to prop up a softening economic recovery. BBC News
