US Federal Reserve Chairman Ben Bernanke says the government may need to inject more capital into banks.
In a speech at the London School of Economics on Tuesday, he said fiscal stimulus alone would not be enough to promote a lasting economic recovery in the United States.
Even though it has cut benchmark interest rates to almost zero, Dr Bernanke said the Fed still has "powerful tools" that could be expanded to spur a rebound.
The US economy has been in recession since December 2007 and the Fed has cut interest rates from 5.25% since September 2007 to stabilise markets and stimulate growth.
He said the Fed would keep the benchmark federal funds rate low for an extensive period to combat the crisis, but stressed that the policy could change if conditions improve.