The dollar added to earlier losses on Wednesday after the Federal Reserve left interest rates unchanged, as was widely expected.
The safe-haven yen and Swiss franc lost some ground as concerns over Britain's referendum on its European Union membership eased.
The U.S. central bank concludes a two-day Federal Open Market Committee meeting later on Wednesday, with Fed Chair Janet Yellen expected to strike a balanced tone, keeping rate hikes in the coming months in play but possibly flagging "Brexit" risks as well.
"No doubt Ms. Yellen and company will make references to the current turbulence caused by the Brexit vote as part of the reason for their cautious approach," said Boris Schlossberg, managing director of FX strategy at BK Asset Management in New York.
"But if they look past this event and suggest that the U.S. economy continues to expand at a healthy pace, the market expectations for a Fed hike in July may increase markedly especially if next month's NFPs (non-farm payrolls) show a rebound in jobs."