Native Mongolian herders claimed that a $5bn (£3.3bn) expansion of the company's Oyu Tolgoi copper and gold mine in the Gobi desert threatened the fresh water supply of hundreds of nomadic people and the area's unique ecology.
Sukhgerel Dugersuren, executive director of Mongolian civil society organisation Oyu Tolgoi Watch, said: "Water is a life and death resource. Rio Tinto is diverting water without the consent of the local community or the government.
"It is already evident that not only livestock but local communities are losing access to adequate water supply. Pasture ... [and] water resources are being taken from us and fenced in by the mine."
She claimed that a tailings pond used to collect waste material from the mine had leaked and told Rio's board that the local community demanded assurances that "there isn't going to be a catastrophe in the region".
Sam Walsh, Rio's new chief executive, said the company was committed to environmental protection and human rights and was closely monitoring the mine's development to "ensure our neighbours have a healthy and prosperous future".
At the company's annual meeting, Walsh said Rio recognised the importance of water and would draw water from a deep level aquifer, not from surface water. He said a seasonal river was being diverted around the mine, but the company would create a new spring for animal grazing and water collection further downstream.
Walsh said the mine, which is 34%-owned by the Mongolian government, would provide a massive boost to the local economy and could represent up to 36% of Mongolia's GDP.
Protesters also raised concerns about Rio's planned mines in Bristol Bay, Alaska, a controversial iron ore mine in Guinea, and a nickel and copper mine in Michigan.
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