WASHINGTON » The average U.S. rate on the 30-year fixed mortgage rose this week to 4.51 percent, a two-year high. Rates have been rising on expectations that the Federal Reserve will slow its bond purchases this year.

Mortgage buyer Freddie Mac says the average on the 30-year loan jumped from 4.29 percent the previous week. Just two months ago, it was 3.35 percent — barely above the record low of 3.31 percent.

The average on the 15-year fixed mortgage rose to 3.53 percent from 3.39 percent last week. That’s the highest since August 2011.

Chairman Ben Bernanke has said the Fed could slow its bond purchases this year if the economy strengthens. The purchases have kept rates low. The yield on the 10-year Treasury, which mortgage rates typically track, has been rising.