The list of “problem” US banks grew by almost 50% in the fourth quarter, the Federal Deposit Insurance Corporation said on Thursday, fanning fears that further bank failures could put the agency’s deposit insurance fund under severe pressure. Sheila Bair, FDIC chairman, suggested more failures were likely despite government support for the industry and warned that proposed increases to the premiums that banks pay for deposit insurance may fall short of the insurance fund’s needs. The FDIC’s board will meet Friday to approve an increase in premiums.