Average US rate on 30-year mortgage falls to 3.66 percent; 15-year rate down to 2.93 percent

Average long-term U.S. mortgage rates declined this week, approaching historically low levels with the spring home-buying season underway.

Mortgage giant Freddie Mac says the national average for a 30-year fixed-rate mortgage slipped to 3.66 percent from 3.70 percent last week.

The average rate for a 15-year mortgage, popular with homeowners who refinance, fell to 2.93 percent from 2.98 percent last week.

A year ago, the average 30-year mortgage rate was 4.34 percent and the 15-year rate was 3.38 percent.

Mortgage rates have remained low even though the Federal Reserve in October ended its monthly bond purchases, designed to hold down long-term rates. The Fed signaled recently that it's still not ready to start raising short-term rates, after keeping them near zero for over six years.