The U.S. dollar spiked to a more than three-week high in the wake of the comments on Tuesday from Federal Reserve Chair Janet Yellen that prompted markets to assign a higher probability to the prospect of an interest rate hike as early as March.

The dollar index posted its fourth positive session in a row and its highest level since January 20 before slipping back only marginally in early trade on Wednesday as Yellen's remarks were interpreted as placing greater emphasis on the possibility of a hike at each upcoming meeting.