U.S. mortgage rates have hit their highest level since 2014, a new challenge for a housing market that has been central to the economic recovery but remains vulnerable to even modest headwinds.

The rate for a 30-year fixed-rate mortgage rose to 4.46%, the highest in more than four years and the ninth consecutive week of increases, according to data Thursday from mortgage-finance giant Freddie Mac. At the start of the year, the average rate was 3.95%.

...