U.S. import prices unexpectedly rose in September to post their largest gain in five months on higher fuel and food costs, according to a government report Friday that pointed to some build-up in imported inflation pressure.

Overall import prices increased 0.3 percent, the Labor Department said, after falling 0.2 percent in August.

Economists polled by Reuters had expected prices to drop 0.3 percent last month. Import prices were up 13.4 percent in the 12 months through September.

Stripping out fuel and food costs, import prices rose 0.3 percent after increasing by the same margin in August.