Inflation remained unchanged in the United States last month on a downturn in energy costs, the US Labour Department said Thursday.

On a seasonally adjusted basis, the consumer price index remained "virtually unchanged" in September from the previous month after seeing its first decrease in two years in August with a fall of 0.1 per cent. Prices increased 4.9 per cent year-over-year, after a 12-month increase of 5.4 per cent in August.

The steady inflation reflected a drop in energy prices, which fell 1.9 per cent in September after dipping 3.1 per cent in August. Food costs rose 0.6 per cent, the same increase as the month earlier.

Core inflation, which does not include food or energy costs, rose 0.1 per cent month-over-month, and was up 2.5 per cent in the past 12 months. The increase had slowed over past months on declines in the prices of automobiles, clothing and airfares and a smaller increase in recreation costs, the department said.