US factories expanded last month at the fastest pace since June 2011 on a jump in orders. The report signals that manufacturing output could strengthen in coming months.

The Institute for Supply Management, a trade group of purchasing managers, said its manufacturing index rose to 55.7 in August from 55.4 in July. That topped the index's 12-month average of 52.

A reading above 50 indicates growth.

A gauge of new orders rose nearly five points to 63.2, the highest level in more than two years. At the same time, production increased more slowly than in July, and factories added jobs at a weaker rate.

The overall improvement contrasts with other recent reports that had pointed to a slowdown in manufacturing.

The ISM's survey found broad-based growth, with 15 out of 18 industries reporting expansion and only one reporting contraction. That suggests that factory production could accelerate this year.

The Federal Reserve will closely examine the report, which comes two weeks before Fed policymakers will decide whether to slow their bond-buying programme. Chairman Ben Bernanke has said the Fed will scale back its purchases this year if the economy continues to grow.

The $85 billion in monthly bond purchases have been intended to keep interest rates low. The jobs report for August, to be released today, is the most important remaining economic report the Fed will consider.

Last month, a Fed report found that factory output dipped in July. But that slip reflected a slowdown in auto production, which many analysts expect to be only temporary.

Companies also cut back in July on orders for long-lasting US factory goods, according to a government report last week. That drop was driven by a sharp fall in demand for commercial aircraft, a volatile category.

But businesses also sharply reduced their orders for capital goods such as computers, electrical equipment and other items. That decline may signal that business investment, an important driver of the economy, could slow.

The economy grew at a modest 2.5% annual rate in the April-June quarter, the Commerce Department estimated last week. That was better than the government's initial estimate of 1.7%. But many economists now think the economy could slip a bit in the July-September quarter to a 2% annual growth rate or less.