JPMorgan Chase & Co. and Citigroup Inc. are expanding in "jumbo" mortgages used to buy the most expensive homes, helping revive a market that shriveled amid a three-year jump in homeowner defaults.

JPMorgan resumed buying new jumbo loans made by other lenders this month, after halting purchases in March, spokesman Tom Kelly said. Borrowers must have checking accounts with the bank, he said.

Citigroup is again offering the loans through independent mortgage brokers, spokesman Mark Rodgers said.

The banks are signaling new interest in a market hobbled since 2007, when defaults on home loans caused investors to flee securities backed by mortgages.

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