Peruvian police on Tuesday arrested 15 activists spearheading a protest against Swiss mining company Xstrata over allegations it is polluting rivers.

Herbert Huaman, head of the Front for the Defense of Espinar and main leader of the movement, was among those detained on the ninth day of demonstrations that have claimed two lives and injured dozens. Images of the arrests were shown on local television.

Hundreds of protesters, including striking miners, have lugged tree trunks and boulders into roads in the Espinar area of Cusco in southern Peru to protest what they say is Xstrata's pollution of the Salado and Canipia Rivers.

They are demanding environmental studies, citing local animal deaths. They also want the company to increase from three to 30 percent the amount of earnings it invests in local economic development.

Prime Minister Oscar Valdes declared a state of emergency late Monday, saying it was needed to "safeguard public security and allow free transit" after two people were killed in clashes with police and a provincial prosecutor was briefly kidnapped.

Shortly before being arrested, Huaman vowed the protests would continue and accused Xstrata of refusing to talk about the protestors' demands.

"We call on President Ollanta Humala to lift the state of emergency to initiate the dialogue and resolve the environmental problems," he said.

Xstrata said its environmental operations complied with all legal requirements but it was willing to undertake extra monitoring "to clarify any perceptions or concerns that the population may have."

It has also said it expressed a willingness to improve on the agreement under which the Tintaya mine invests three percent of earnings locally.

Xstrata operates four copper mines in Peru, two of which are currently being developed.