Protests against a copper mining project in southern Peru injured a dozen people and spread to other parts of the region.
Demonstrators in Cocachacra, at the epicentre of the conflict, threw stones at police, who responded with tear gas.
Twelve people were reported injured, and authorities said protests had erupted in other cities, including the regional capital of Arequipa.
Residents of the southern coastal valley are opposing the £887 million Tia Maria project of Mexican-owned Southern Peru Copper.
Farmers fear the project would contaminate their crops. The owners say it would use desalinated water and pump water used in processing into the Pacific Ocean.
The protests, which began in March, have claimed the lives of two civilians and a police officer.
“A strike lasts 48 hours – it is not normal for it to last 53 days,” said the head of the police operation, Enrique Blanco.