Associated Press (AP) -- The average rate on a 30-year mortgage in the U.S. rose slightly for the second week in a row, a modest setback for prospective home shoppers as the spring homebuying season ramps up.

The rate rose to 6.67% from 6.65% last week, mortgage buyer Freddie Mac said Thursday. A year ago, the rate averaged 6.87%.

Including this week, the average rate on a 30-year home loan has risen only twice in the past nine weeks, a welcome trend for aspiring homebuyers struggling to afford a home after years of soaring home prices.

"The 30-year fixed-rate mortgage has stayed under 7% for nine consecutive weeks, which is helpful for potential buyers and sellers alike," said Sam Khater, Freddie Mac's chief economist.

Borrowing costs on 15-year fixed-rate mortgages, popular with homeowners refinancing their home loans, also rose this week, pushing the average rate to 5.83% from 5.8% last week. A year ago, it averaged 6.21%, Freddie Mac said.

Mortgage rates are influenced by several factors, including bond market investors' expectations for future inflation, global demand for U.S. Treasurys and the Federal Reserve's interest rate policy decisions.

After climbing to just above 7% in mid-January, the average rate on a 30-year mortgage has been mostly declining, loosely following the moves in the 10-year Treasury yield, which lenders use as a guide to pricing home loans.