San Francisco Federal Reserve President John Williams restated his view that an improving economy would allow the central bank to wind down its bond-buying program this summer, but low inflation needs to be closely watched, Reuters reports.

"It really is a question for me of watching for continuing signs in the U.S. labour market, continuing signs of more greater confidence in the momentum in the U.S. economy, but also watching carefully where the underlying inflation rate is and what the outlook for inflation is," Williams told reporters during a visit to Sweden.