The U.S. Federal Reserve is considering expanding one of its lending programs to include commercial mortgage-backed securities with terms longer than three years, a Fed official said on Friday.

The official, who spoke on condition of anonymity because the decision has not been finalized, said the central bank may start accepting the broader array of collateral in the coming months.

The Fed has been considering how best to accept commercial mortgage-backed securities as collateral for lending under its Term Asset-Backed Securities Lending Facility, known as TALF, one of a myriad of programs the central bank has launched to try to revive the economy.

The investment community has been pushing for the Fed to accept securities with a five-year term, but the central bank is concerned about holding longer-term assets on its balance sheet because that can make it more difficult for it to pull back on lending once the economy recovers.

Investors are increasingly concerned about the risk of rising defaults in commercial real estate. General Growth Properties Inc , the second-largest U.S. mall owner, declared bankruptcy on Thursday in the biggest real estate failure in U.S. history, signaling the possibility of more failures to follow as consumer spending remains muted.

TALF is designed to help restore the flow of credit to the economy, and has focused initially on consumer credit. It accepts asset-backed securities tied to a variety of loans including auto and small business loans as well as credit card debt.

(Reporting by Mark Felsenthal; Writing by Emily Kaiser; Editing by Theodore d'Afflisio)