Applications for U.S. home mortgages jumped last week on a surge in demand for refinancings, though purchase activity edged down, an industry group said on Wednesday.

The Mortgage Bankers Association said its seasonally adjusted index of mortgage application activity, which includes both refinancing and home purchase demand, climbed 16.9 percent in the week ended July 13.

The MBA's seasonally adjusted index of refinancing applications posted the biggest jump in seven months, rising 21.6 percent as mortgage interest rates hit record lows.

But the gauge of loan requests for home purchases, a leading indicator of home sales, dipped 0.1 percent.

The refinance share of total mortgage activity rose to 80.1 percent of applications from 77 percent the week before.

Fixed 30-year mortgage rates fell to yet another record low, averaging 3.74 percent and down 5 basis points from 3.79 percent.

The survey covers over 75 percent of U.S. retail residential mortgage applications, according to MBA.