St. Louis Fed President James Bullard said in a speech on Thursday that the recent drop in oil prices may weigh on the timing when the Fed's 2% inflation target will be reached.

"Low inflation expectations may keep actual inflation lower, all else equal, making it more difficult for the Fed to return inflation to target," he said.

"Headline inflation will return to target once oil prices stabilize, but recent further declines in global oil prices are calling into question when such a stabilization may occur," Bullard added.

St. Louis Fed president pointed out that "low oil prices remain a net positive for the U.S. economy".

Bullard is a voting member of the Federal Open Market Committee (FOMC) this year.