WASHINGTON (AP) — Average long-term U.S. mortgage rates jumped this week to their highest levels this year, with the key 30-year rate topping 4 percent for the first time since late 2014.

Rates have been surging amid signs of improvement in the economy, which have pushed bond yields higher. Mortgage rates often follow the yield on the 10-year Treasury note, which reached a high for the year of 2.49 percent Wednesday.

The increase in mortgage rates has come during the height of the spring home buying season.

Mortgage giant Freddie Mac says the average rate on a 30-year fixed-rate mortgage climbed to 4.04 percent this week from 3.87 percent a week earlier. The rate on 15-year fixed-rate mortgages increased to 3.25 percent from 3.08 percent.