WASHINGTON — Rates on 30-year mortgages kept surging this week, rising to the highest level in nearly nine months, reflecting more concerns about what the Federal Reserve will do about a rising inflation threat.

Mortgage company Freddie Mac reported yesterday that 30-year fixed-rate mortgages averaged 6.42 percent this week. That was up sharply from 6.32 percent last week.

It marked the fourth straight week that the mortgages have been above 6 percent.

Other types of mortgages showed increases this week, according to the Freddie Mac survey. Rates on 15-year fixed-rate mortgages rose to 6.02 percent, up from 5.93 percent last week.

Five-year adjustable-rate mortgages rose to 5.89 percent, up from 5.70 percent. The rate on a one-year adjustable-rate mortgage rose to 5.19 percent, up from 5.09 percent last week.