WASHINGTON » Average U.S. rates for fixed mortgages rose this week to their highest levels in two years, driven by heightened speculation that the Federal Reserve will slow its bond purchases later this year.

Mortgage buyer Freddie Mac says the average rate on the 30-year loan jumped to 4.58 percent, up from 4.40 percent last week. The average on the 15-year fixed loan rose to 3.60 percent from 3.44 percent. Both averages are the highest since July 2011.

Rates have risen more than a full percentage point since May. Last week’s spike comes after more Fed members signaled they could be open to reducing the bond purchases as early as September. The purchases have helped keep long-term interest rates low, including mortgage rates.