Interest rates on 30-year fixed-rate mortgages fell for the first time in three weeks, real estate website Zillow.com said on Tuesday.

Interest rates are historically low, offering a glimmer of hope for a housing market that still faces plenty of obstacles. Rock-bottom rates may boost home loan refinancing activity and also makes homes more affordable.

Mortgage rates on 30-year fixed mortgages, the most widely used loan, were 4.25 percent Tuesday afternoon, down from 4.32 percent at the same time last week, according to Zillow Mortgage Marketplace.

That is the lowest rate reported since Zillow Mortgage Marketplace launched in April 2008.

The 30-year fixed mortgage rate peaked at 4.35 percent on Saturday and hovered near 4.33 percent before falling on Monday to the current rate, Zillow said.

Interest rates on other types of mortgages also fell.

Fifteen-year fixed mortgage rates were 3.73 percent, down from 3.76 percent the prior week. Rates for 5/1 adjustable-rate mortgages, or ARMs, set at a fixed rate for five years and adjustable each following year, were 3.13 percent, down from 3.27 percent the prior week.

Zillow's rates are based on thousands of custom mortgage quotes submitted daily to anonymous borrowers through the website. They are not marketing rates, or a weekly survey.

Mortgage rates are linked to yields on Treasuries and yields on mortgage-backed securities. Yields move inversely to price.

Mortgage rates may continue to head lower.

Treasuries rallied on Tuesday as investors stampeded into safe-haven long-term U.S. debt.

Mortgage