WASHINGTON (AP) — Long-term U.S. mortgage rates climbed this week to their highest average in more than four years, ratcheting up affordability pressures at the start of the traditional spring home buying season.

Mortgage buyer Freddie Mac says the average rate on 30-year fixed-rate mortgages climbed to 4.46 percent this week from 4.43 percent last week. This marks the highest average since January 2014. The 30-year rate averaged 4.21 percent a year ago.

The average rate on 15-year, fixed-rate loans rose to 3.94 percent from 3.90 percent last week.

Mortgage rates have been heading upward for the past nine weeks. The recent increases have come even as the yield on the 10-year Treasury note has stayed below its two-week high of 2.95 percent.