St. Louis Fed President James Bullard wrote in a letter on Thursday that the Fed should continue to raise its interest rate.

"Even if the Fed continues to raise interest rates, U.S. monetary policy will remain exceptionally accommodative," he said.

"A key reason for normalizing policy is that the FOMC's goals regarding inflation and employment have essentially been met," St. Louis Fed president added.

Bullard pointed out that low interest rates for a longer period could lead to a bubble in asset prices.