US central bankers say they may need to increase the key lending rate "fairly soon," but are concerned about the uncertainty of President Donald Trump's tax and spending policies, according to the minutes of their last meeting published Wednesday.

Federal Reserve officials said their outlook for the economy and interest rates had not changed much since December, when they indicated three rate hikes were likely this year.

They still expect to only need gradual rate increases if the economy continues to grow at a moderate pace, according to the minutes of the January 31-February 1 monetary policy meeting.