In a relatively downbeat assessment of the economy, Mr Bernanke said: "US economic growth so far this year looks to have been somewhat slower than expected."

His comments sent US stocks falling. The Dow Jones Industrial Average closed down 12.15 points at 12,070.81, having been up until he started his speech.

Speaking at the International Monetary Conference in Atlanta, Mr Bernanke said: "Aggregate output increased at only 1.8pc at an annual rate in the first quarter, and supply chain disruptions associated with the earthquake and tsunami in Japan are hampering economic activity this quarter. A number of indicators also suggest some loss of momentum in the labour market.

"Until we see a sustained period of stronger job creation, we cannot consider the recovery to be truly established."