Rio's Iron Ore of Canada division was hit by a colder-than-average winter, which disrupted mining in Labrador over the quarter, while port closures due a cyclone late last year reduced shipments in Australia, the company said.
Overall iron ore shipments in the first quarter came in at 66.7 million tonnes.
Rio Tinto said it would draw on its Australian stocks of iron ore to enable it to increase shipments ahead of production, with around 5 million tonnes of inventory drawdown expected in 2014.
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Production of 295 million tonnes in 2014 would keep Rio Tinto ahead of rivals BHP Billiton and Fortescue Metals Group, which report quarterly data on Wednesday.
Iron ore of Canada (IOC) is 59 percent owned by Rio Tinto, 26 percent by Mitsubishi and 15 percent by Labrador Iron Ore Royalty. Rio Tinto put its stake in IOC up for sale about a year ago but offers came in well below the mining group's target of about $3.5 to $4 billion, sources said.
Outside of iron ore, Rio Tinto said mined copper production benefited from richer ore grades at the Kennecott Utah business and output from the recently-opened Oyu Tologoi mine in Mongolia.
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"This more than offset the elimination of production from copper assets divested in 2013," the company said.
Mined copper production was up 17 percent in the first quarter versus a year ago, but fell 6 percent from the previous quarter, it said.