U.S. import prices climbed an unexpectedly steep 1.3 percent in January as the cost of imported petroleum shot up 6.4 percent, its first increase in four months, the Labor Department said on Thursday.

The rise in import prices, which followed a revised 0.1 percent December drop, outstripped expectations on Wall Street for a 0.9 percent gain. But non-petroleum import prices edged up just 0.2 percent last month.

Export prices rose 0.7 percent, ahead of the 0.2 percent gain economists had expected.

The department said crude oil import prices surged 8 percent in January, bringing their increase over the past 12 months to a hefty 48.2 percent.

The sharp rise in oil costs over the past year has pushed overall import prices up sharply and has heightened inflation worries at the Federal Reserve.

In the 12 months through January, import prices were up 8.8 percent, accelerating from the 8 percent gain in the 12-month period ended in December.

Both capital goods and auto import prices declined 0.1 percent in January. The cost of consumer goods imports, excluding autos, edged up 0.2 percent.