United States Steel Corp reported a first-quarter loss, compared with a year-earlier adjusted profit, as its sales dropped more than 10 percent.

The Pittsburgh-based steelmaker's flat-rolled segment, its biggest business unit, recorded an operating loss of $13 million, compared with a year-earlier profit of $183 million, as prices and shipments slipped.

U.S. Steel said flat-rolled results were held back in part by operating costs that rose from the fourth quarter of 2012, reflecting "the absence of several smaller favorable fourth quarter items."

Net loss for the first quarter narrowed to $73 million, or 51 cents a share, from $219 million, or $1.52 a share, a year earlier. Net sales fell to $4.60 billion from $5.17 billion.

Excluding a charge related to the repurchase of some of the company's convertible notes and other items, U.S. Steel reported a loss of $51 million, or 35 cents a share, compared with adjusted earnings of $110 million, or 67 cents a share.

Analysts, on average, had been expecting a loss of 19 cents a share on revenue of $4.66 billion, according to Thomson Reuters I/B/E/S.

U.S. Steel's shares dropped 3.1 percent to $17 in premarket trading in New York.