Bernanke told Congress he still believed unrest in Libya and elsewhere in the oil-rich region would result in "temporary" and "modest" increases in US prices, but acknowledged greater risks remain.

"The most likely outcome is that the recent rise in commodity prices will lead to, at most, a temporary and relatively modest increase in US consumer price inflation," the central bank chief told lawmakers.

"That said, sustained rises in the prices of oil and other commodities would represent a threat both to economic growth and to overall price stability."

He added there was a particular risk from unrest pushing up expectations of future price rises.