The US economy is regaining strength, but questions remain at the pace of recovery, a key survey has revealed.

The Federal Reserve, the US central bank, reported that "almost all" its district offices had reported "signs of improvement or actual increases in economic activity".

But, publishing its latest so-called Beige Book report, the Fed warned that its Cleveland researchers had found that the pace of recovery had "slowed considerably".

"While the overall tone was positive, a few districts expressed qualifications about the pace of the recovery or the strength of their regional economies," the Fed said.

The report's cautious tone was seen as rendering the Fed unlikely to raise US interest rates at its next monthly meeting, in May.

Factory cheer

The Beige Book confirmed observations that consumer spending was solid, with retail sales steady or higher in most districts.

Manufacturers in all areas saw conditions improve.

"Manufacturers were generally optimistic about the outlook for factory activity later in the year," the Fed said.

"Purchasing managers in the New York district, in fact, reported their highest expectations for increases since mid-2000."

But the conditions in the labour market remained mixed.

"Demand for labour showed signs of firming in several districts but was still reported as weak in others."