U.S. consumer prices rose less than expected in July, pointing to benign inflation that could make the Federal Reserve cautious about raising interest rates again this year.

The Labor Department said on Friday the Consumer Price Index edged up 0.1 percent last month after being unchanged in June. That lifted the year-on-year increase in the CPI to 1.7 percent from 1.6 percent in June.

Economists polled by Reuters had forecast the CPI rising 0.2 percent in July and climbing 1.8 percent year-on-year.

Stripping out the volatile food and energy components, consumer prices gained 0.1 percent for the fourth straight month. The so-called core CPI rose 1.7 percent in the 12 months through July – it has now increased by the same margin for three straight months.

The modest gain in consumer prices could worry Fed officials who have largely viewed the retreat in inflation as temporary.

Fed Chair Janet Yellen told lawmakers last month that “some special factors,” including prices for mobile phone plans and prescription drugs were partly responsible for the low inflation readings.

The U.S. central bank has a 2 percent inflation target and tracks a measure that has been stuck at 1.5 percent since May. Inflation remains tame despite the labor market being near full employment, a conundrum for the Fed as it contemplates tightening monetary policy further.

The central bank is expected to announce a plan to start reducing its $4.2 trillion portfolio of Treasury bonds and mortgage-backed securities at its policy meeting next month. It is expected to delay its next rate hike until December while it monitors inflation. The Fed has raised borrowing costs twice this year.

Last month, gasoline prices were unchanged after tumbling 2.8 percent in June. Food prices rose 0.2 percent after being unchanged in June. The cost of rental accommodation increased 0.2 percent in July after rising 0.3 percent in the prior month.

Owners’ equivalent rent of primary residence rose 0.3 percent after advancing by the same margin in June.

The cost of mobile phone services fell 0.3 percent last month after decreasing 0.8 percent in June.

Prescription drugs jumped 1.3 percent in July after increasing 1.0 percent in the prior month. Prices for apparel rose 0.3 percent after four straight months of declines. The cost of new motor vehicles fell 0.5 percent, marking the sixth consecutive monthly decline.