U.S. mortgage rates fell again in the past week, with the average rate on 30-year and 15-year fixed-rate mortgages furthering record lows, according to Freddie Mac's weekly survey of mortgage rates.

Rates have remained at or near record lows as the Treasury market has rallied amid stock-market volatility. A rally in Treasurys pushes yields lower, and mortgage rates generally track those yields.

The 30-year fixed-rate mortgage averaged 4.54% for the week ended Thursday, down from the prior week's 4.56% and 5.25% a year ago. The rate sits at the lowest point since Freddie began tracking it in 1971.

Rates on 15-year fixed-rate mortgages were 4%, down from 4.03% and 4.69%, respectively. It is at the lowest point since 1991, when Freddie started tracking it.

Five-year Treasury-indexed hybrid adjustable-rate mortgages averaged 3.76%, lower than the prior week's 3.79% and 4 ...