The long period of low interest rates is unprecedented and some members of the policy-making Open Markets Committee signalled that they do not expect interest rates to start rising until 2015 or 2016.

The interest rate projections suggest that the Fed and its chairman Ben Bernanke are far from confident that America has fully recovered from the 2008 financial crisis and recession despite 15 unbroken months of falling unemployment.

The Fed's caution was demonstrated by its decision to lower its projected growth range for the US economy to 2.2pc to 2.7pc against the previous figures of 2.5pc to 2.9pc.

But the it is hopeful that a combination of low interest rates and modest growth will be enough to keep the unemployment rate dropping.

It believes that the jobless rate will end the year at 8.2pc to 8.5pc of the total workforce, down from its previous estimate of 8.5pc to 8.7pc.

The continued progress on the jobs front will be seen as helpful to President Barack Obama as he seeks re-election in November.

For the first time the Fed has set an inflation target of 2pc. This brings its operations in line with other major central banks, including the Bank of England, which have a single target for price rises. But the Fed declined to set a target for employment even though, unlike other central banks, it has a specific mandate to create jobs.

The US central bank unveiled its new projections for the US economy as Britain's business leaders cited the Eurozone crisis as their main concern.

The Confederation of British Industry's Industrial Trends Survey found that a balance of 15pc more employers said new orders had fallen in the quarter to December. This compares with a 6pc rise when the survey was last conducted in October.

Both domestic and export orders fell for the first time in two years, the report said.

The survey found that 39pc of businesses said that political and economic conditions abroad, mainly concerning European sovereign debt, were a constraint on activity. That is almost double the usual proportion of firms citing such worries.

However, the survey found that business leaders were more positive about the coming three months because the US recovery was proving to be stronger than expected.