UPDATE 1-Miner Cliffs posts loss on lower iron ore, coal prices

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April 24 (Reuters) - Cliffs Natural Resources Inc, which is facing off against an activist investor who wants to break up the company, reported a first-quarter loss on Thursday on the back of lower market prices for iron ore and metallurgical coal.

The U.S.-based miner reported a net loss of $83 million, or 54 cents a share, in the three months to end-March from a net profit of $97 million, or 66 cents a share, in the same period a year earlier.

Revenue fell 18 percent to $940 million, hurt by the price declines as well as a 2 percent decrease in global iron ore sales volumes, which Cliffs blamed on harsh winter weather in North America.

Cliffs said it is maintaining its full-year sales and production volumes for all business segments.

The Cleveland, Ohio-based company is being targeted by hedge fund Casablanca Capital, following several quarters of weak earnings and share performance. Its stock is down 80 percent in the past three years.

Casablanca argues that the company's international assets are weighing on its cash-generating U.S. business and should be spun off. The New York-based fund wants to install a new chief executive at Cliffs as well as a majority of new directors.

Weakness in the steel market has hit relatively high-cost iron ore suppliers like Cliffs hard.

(Reporting by Nicole Mordant in Vancouver; editing by Matthew Lewis)