The United States and Japan may need to shore up bank oversight to prepare for economic downturns, the head of the Federal Reserve Bank of Boston warned.

Eric Rosengren, president of the Boston Fed, said in a speech that policymakers in the two major economies should consider whether regulators need more tools, including requiring banks to hold more capital now, to counteract economic risks.

"Japan, like the United States, might benefit from considering an expanded set of macroprudential tools to enhance the financial system's resilience," Rosengren said.

Rosengren, who is voting member of the Fed this year on U.S. interest rates, did not discuss his monetary policy outlook in the speech.