Consumer confidence in the US fell unexpectedly in August as higher interest rates and a dip in the rate of economic growth appeared to sap optimism.

The Thomson Reuters/University of Michigan's preliminary reading of consumer sentiment slipped from a six-year high of 85.1 in July to 80.0. The figure was well below the 85.5 reading expected by economists.

Friday's figure follows a series of disappointing results from US retailers including Walmart and Macy's that have caught economists by surprise. "The expectation was that we were going to have a good August," said economist Ken Goldstein of the Conference Board. "Clearly that was wrong."

But Goldstein said the figure was more likely a "bump in the road" than a sign that the recovery was taking a downturn.

Consumers' view of current economic conditions showed the biggest decline in the Michigan survey, falling to 91.0 from 98.6. But most maintained "the prevailing view that the economic expansion will continue", survey director Richard Curtin said in a statement.

"Perhaps the most important recent changes have been the increase in home values as well as the jump in the numbers that expect interest rate increases during the year ahead," he said.

Long-term interest rates have risen by more than a full percentage point over the last three months as the Federal Reserve has been signaled it is preparing to scale back its $85bn-a-month bond buying programme.

Fears that the Fed could start scaling back as early as next month pushed up mortgage rates, a potential drag on housing recovery. Stock markets too were jolted this week by fears that the Fed was preparing to act.

"The figure is a surprise but the trend is still towards improving consumer confidence and spending," said Goldstein. "Back to school sales have been disappointing but I think it would be premature to think this improving trend is coming to an end."