Charles Plosser, President and CEO of the Federal Reserve Bank of Philadelphia

The Federal Reserve should be more explicit about the likely future path of interest rates, a top Fed official said on Tuesday, saying that while the central bank's recent changes to guidance on interest rates are a step in the right direction they do not go far enough.

The U.S. central bank in December promised to keep rates near zero until unemployment falls to 6.5 percent, as long as inflation does not threaten to rise above 2.5 percent. Its policy-setting panel, the Federal Open Market Committee, or FOMC, also said it would keep policy highly accommodative for a "considerable time" after the recovery strengthens, rather than tightening policy immediately.