US payrolls rose far less than expected in March, keeping the door open for further monetary policy support from the Federal Reserve, even as the unemployment rate fell to a three-year low of 8.2%.

Employers added 120,000 jobs last month, the US Labor Department said today, the smallest increase since October.

Economists polled by Reuters had expected non-farm employment to increase 203,000 and the jobless rate to hold at 8.3%.

The slowdown in employment growth last month likely reflected the fading boost from unseasonably warm winter weather.

It supported the caution on the jobs market from Fed Chairman Ben Bernanke last week.

Mr Bernanke expressed doubts the recent job gains could be sustained, and March's weak report was in line with expectations that economic growth slowed to an annual pace of 2%in the first quarter from the 3% rate in the October-December period.

"This is going to keep the Fed in easy policy mode. They're going to want to see a step toward 300,000 before they start to think about seeing a stronger outlook for the economy," said Sean Incremona, an economist at 4CAST in New York.

S&P 500 stock index futures dropped sharply after the data, while US Treasury debt prices turned higher. The dollar turned lower versus euro.

While the unemployment rate fell to its lowest level since January 2009, that was mainly because some people gave up the search for work. The separate household survey, from which the jobless rate is derived also showed a drop in employment.

The unemployment rate has fallen from 9.1% in August.

The weak employment gains could hurt President Barack Obama's chances for re-election in November.

The weakness in hiring last month was concentrated in the vast private services sector, which added only 90,000 after increasing payrolls by 204,000 in February. Retail employment fell dropped 33,800 after falling 28,600 the prior month.

Construction hiring fell 7,000, the second straight monthly decline. Temporary help fell 7,500 after rising 54,900 in February.

However, manufacturing enjoyed another month of strong job gains, with factories adding 37,000 new positions, helped by carmakers trying to meet pent-up demand for motor vehicles. Factory jobs increased by 31,000 in February.

Government employment edged down 1,000 after rising 7,000 in February. Despite the weak employment gains last month, average hourly earnings rose 5 cents.

The workweek dipped to 34.5 hours from 34.6 hours in February.