'Economy levelling'

As part of that strategy, he flooded financial markets with hundreds of billions of dollars in federal money and led the effort to rescue failing financial institutions such as Bear Stearns and AIG.

Last week, Bernanke said there were positive signs that the world economy would start to grow, following the worst global downturn in decades.

"After contracting sharply over the past year, economic activity appears to be levelling out, both in the United States and abroad," he told central bankers at a meeting in the western US state of Wyoming.

But Bernanke has also faced criticism from politicians who say he has gone too far in extending federal control over the US financial system.

Bernanke, 55, was appointed Federal Reserve chairman by George Bush, the former US president, in 2006.