Average U.S. rates on fixed mortgages rose this week in the wake of comments by Federal Reserve Chairman Janet Yellen suggesting that the Fed could start raising short-term interest rates by mid-2015.

Mortgage buyer Freddie Mac said Thursday the average rate for the 30-year loan increased to 4.40 percent from 4.32 percent last week. The average for the 15-year mortgage rose to 3.42 percent from 3.32 percent.