Federal Reserve chairman Ben Bernanke has reiterated his concerns about high levels of US unemployment, just days after a surprisingly large drop in the jobless rate.

Figures last week showed that the US unemployment dropped to 8.3% - the lowest level in two years - in January. But Bernanke said the market had improved only "modestly" over the last year.

"We have a long way to go before the labour market can be said to be operating normally,' Bernanke told the Senate Budget Committee. He said the high level of long-term unemployment was particularly worrying, as more than 40% of the unemployed have been out of work for at least ten months.

Bernanke sought to dodge a highly-charged political debate over the exact meaning of recent jobs data, which has been picked over by Republicans and Democrats as they look to November's general election.

But he appeared to agree with Republican assertions, echoed by presidential frontrunner Mitt Romney, that many more than the official figure of 12.8 million Americans are unemployed or underemployed, and that many people have stopped looking for a job all together.

But he also insisted that the overall picture was brightening and the country was moving toward the longer-run normal rate of unemployment of between 5.2% and 6%.