The death toll in an attack on a copper mine encampment in northern Peru has risen to three, Interior Minister Octavio Salazar said Tuesday.

Between 15 to 20 armed assailants attacked the mine site run by Rio Blanco, a subsidiary of British company Monterrico Metals and Chinese company Zijin, on Sunday morning, Salazar said.

An investigation into the attack is under way and a police team from Lima has been dispatched to the site, where two people were also reported missing after the incident.

Site manager Jian Wu said the assailants had not been identified, but ruled out the possibility that the attack was the work of locals, many of whom oppose the mine on environmental grounds, suggesting instead that it could be related to drug trafficking.

The attack has raised tensions in Peru's mining industry -- a key economic sector for the country -- coming as a group of locals in the southeastern Cusco region have taken over a separate encampment at the Ares mine.

Company manager Ernesto Balerezo reported the takeover Tuesday and denied accusations that the mine site was contributing to environmental degradation.

Jorge Chavez, leader of the Defense Front of Chumbivilcas, said the mine was contaminating the local river.

- Our animals are being killed, our alpacas and vicunas, and the trout are disappearing from the river - he said.