Fewer Federal Reserve officials expect the central bank to raise interest rates more than once this year, as policy makers painted a mixed picture of a U.S. economy where growth is picking up while job gains slow.

Britain's June 23 referendum on membership of the European Union was also "one of the uncertainties that we discussed and that factored into today's decision," Chair Janet Yellen said after the Federal Open Market Committee voted unanimously to leave rates steady at the end of a two-day meeting on Wednesday in Washington.

"It is a decision that could have consequences for economic and financial conditions in global financial markets," she told a press conference following the meeting. "If it does so, it could have consequences in turn for the U.S. economic outlook that would be a factor in deciding on the appropriate path of policy."