US job growth increased less than expected in April and the unemployment rate dropped to near a 17-1/2-year low of 3.9% as some jobless Americans left the labour force.

The Labour Department's closely watched employment report also showed wages barely rose last month, which could ease concerns that inflation pressures are rapidly building up, likely keeping the Federal Reserve on a gradual path of monetary policy tightening.

Non-farm payrolls increased by 164,000 jobs last month, the Labour Department said.

Data for March was revised up to show payrolls rising by 135,000 jobs instead of the previously reported 103,000.

That was still the fewest amount of jobs created in six months and followed an outsized gain of 324,000 in February.

While cold weather in March and April probably held back job growth, hiring is moderating as the labour market hits full employment.

There has been an increase in reports of employers, especially in the construction and manufacturing sectors,struggling to find qualified workers.

The drop of two-tenths of a percentage point in the unemployment rate from 4.1% in March pushed it to a level last seen in December 2000 and within striking distance of the Fed's forecast of 3.8% by the end of this year.

It was he first time in six months that the jobless rate dropped.

But 236,000 people left the labour force in April.

The labour force participation rate, or the proportion of working-age Americans who have a job or are looking for one, fell to 62.8% last month from 62.9% in March.

Economists polled by Reuters had forecast payrolls rising by 192,000 jobs in April and the unemployment rate falling to 4%.

Longer-dated US Treasury yields fell after the data. The dollar pared losses against a basket of currencies and US stock index futures trimmed losses.