US consumer price gains slowed unexpectedly last month, continuing a softening trend since the summer that could ease some investor fears of accelerating interest rate hikes.

The report came amid a deepening global sell-off in equities as investors dumped stocks on worries about rising bond yields, international trade conflict and gradually tightening monetary policy.

Falling energy and flat prices for food weighed on the Consumer Price Index, which tracks the costs of household goods and services, according to the Labor Department data. 

The US consumer price index rose 0.1% in September compared to the previous month, a tenth of a point below a consensus forecast, marking the smallest monthly gain since June. 

But the index for used cars, which had risen in late 2017 as Americans replaced cars destroyed in natural disasters, tumbled by 3%. 

Compared to prices in September of last year, CPI slowed to 2.3%, down four tenths from the 2.7% recorded in August and the weakest reading since February. 

Excluding the volatile food and fuel categories, the "core" index also gained 0.1% for the second month in a row, driven by increases in costs for clothing, auto insurance and airfare. 

Year over year, core CPI rose 2.2% the same as August, leaving it four tenths above February. 

President Donald Trump has blamed the Federal Reserve for the crumbling stock markets, calling its recent interest rate hikes "crazy" and saying it was "making a big mistake" by being "too aggressive." 

However, with US unemployment now well below 4%, economists say a brief pause in consumer prices is unlikely to convince policymakers that it no longer has to worry about inflation.