WASHINGTON - Average long-term U.S. mortgage rates crossed the 4 percent mark this week, a slight increase in the wake of the Federal Reserve decision this month to hike a key short-term interest rate.

Mortgage buyer Freddie Mac says the average rate on a 30-year fixed-rate mortgage rose to 4.01 percent from 3.96 percent a week earlier. That rate has risen from its 3.87 percent average a year ago and has been steadily increasing since late October.

Still, borrowing costs are well below historic averages of 6 percent 30-year mortgage rates.

The average rate on 15-year fixed-rate mortgages increased to 3.24 percent from 3.22 percent.