US consumer prices rose marginally in September as energy costs fell broadly, painting a weak inflation picture that should give the Federal Reserve ample room to keep interest rates low for a while.

The Labor Department said on Wednesday its Consumer Price Index edged up 0.1 per cent last month after declining 0.2 per cent in August.

The CPI increased 1.7 per cent in the 12 months through September after a similar rise in August. The CPI-W index, which is used to make adjustments for Social Security payments rose 1.7 per cent in the third quarter from the year earlier.

Inflation has waned in recent months after quickening in the second quarter, in part as a strengthening dollar and slower economic growth in China and the euro zone dampen imported price pressures.

Weak inflation and a recent global equities market sell-off could see the US central bank in no rush to start raising its benchmark overnight interest rate, which it has kept near zero since December 2008.

Financial markets now expect the first interest rate hike in the fourth quarter of 2015 instead of the second quarter.

Stripping out food and energy prices, the so-called core CPI ticked up 0.1 per cent last month after being unchanged in August. In the 12 months through September, the core CPI rose 1.7 per cent after advancing by the same margin in August.

The Fed targets 2 per cent inflation and it tracks an index that is running even lower than the CPI.

In September, energy prices fell for a third straight month, with gasoline prices slipping 1 per cent after dropping 4.1 per cent in August. Food prices gained 0.3 perc ent after rising 0.2 perc ent in August.

Within the core CPI, shelter costs increased 0.3 per cent in September after rising 0.2 per cent in August. The shelter index was up 3 per cent in the 12 months through September, the largest gain since January 2008.

Airline fares declined for a third straight month, while prices for new motor vehicles and apparel were unchanged.

Reuters