The US Federal Reserve has kept interest rates at between 0.25% and 0.5% in the face of an uncertain jobs market.
The possibility of Brexit was one of the factors that led the US Federal Reserve to keep interest rates on hold, Chair Janet Yellen said.
The US central bank also said it expected a "slower path" for future rate rises.
It raised rates in December for the first time in nearly a decade.
On the 23 June UK referendum on whether to stay in the European Union, Ms Yellen said: "Clearly this is a very important decision for the United Kingdom and for Europe.
"It is a decision that could have consequences for economic and financial conditions in global financial markets.
"If it does so it could have consequences in turn for the US economic outlook that would be a factor in deciding on the appropriate path of policy," she added.
Fed policymakers did not reveal when rates might rise, but the door has been left open for an increase when they next meet at the end of July.
Chair Yellen added: "Proceeding cautiously and raising our interest-rate target will allow us to verify that economic growth will return to a moderate pace, that the labor market will strengthen further, and that inflation will continue to make progress toward our 2% objective."
The Fed said in a statement that the pace of improvement in the labour market had slowed. The bank added, however, that "economic activity will expand at a moderate pace and labour market indicators will strengthen" even with gradual rate increases.
