WASHINGTON -

Average U.S. rates for 30-year and 15-year fixed mortgages fell to fresh record lows this week, offering more incentive for Americans to buy or refinance homes.

Mortgage buyer Freddie Mac said Thursday that the rate on the 30-year loan fell to 3.84 percent, the lowest since long-term mortgages began in the 1950s. That's below the previous record rate of 3.87 percent reached in February.

The 15-year mortgage, a popular option for refinancing, dropped to 3.07 percent, also a record. The previous record of 3.11 percent was hit three weeks ago.

Cheaper mortgage rates haven't boosted home sales. Rates have been below 4 percent for all but one week since early December. Yet sales of previously occupied homes and new homes fell in March.

Analysts suspect that some of that weakness reflected a warm winter, which pulled sales that would normally occur during the spring buying season into January and February.

Still, many potential buyers can't qualify for loans or afford higher down payments required by banks. Home prices in many cities continue to fall, making those that can afford to buy uneasy about entering the market. Many who can afford to buy or refinance have already taken advantage of lower rates.