WASHINGTON (AP) — Average U.S. rates on fixed mortgages rose this week but stayed near their historic lows. Cheaper mortgages have helped the economy by spurring more home-buying and refinancing.

Mortgage buyer Freddie Mac says the average rate for the 30-year loan increased to 3.51 percent from 3.42 percent last week. That's still near the average of 3.31 percent reached in November, the lowest on records dating to 1971.

The average on the 15-year loan rose to 2.69 percent. That's up from 2.61 percent last week, which was the lowest on records going back to 1991.

Low mortgage rates have helped sustained the housing recovery that began last year. Home sales and construction are up from a year ago, and prices are rising in most U.S. markets.