The killing of an anti-mining activist by a motorcycle gunman has led investigators to question staff at a Canadian-owned mine in southern Mexico, a spokesman for the company said Wednesday.

Mariano Abarca Robledo was shot in the head and chest on Friday in the town of Chicomuselo, near the Guatemalan border, said Gustavo Castro, an activist who worked with Abarca Robledo organizing opposition to barite mining in the region.

A spokesman for Calgary-based Blackfire Exploration Ltd. said the company had no involvement in the death. He spoke on condition of anonymity, citing advice from his attorney.

The spokesman said Blackfire has asked the Canadian Embassy in Mexico to intervene after receiving allegations that their Chiapas mine employees were being attacked and beaten in response to the killing.

Canadian Embassy spokeswoman Gabriela Hernandez in Mexico City said that Canada "regrets this act of violence but the Embassy of Canada is not involved in the investigation. It is a matter for Mexican officials."

Robledo feared for his life

Activists said that Abarca Robledo feared for his life and recently told police that Blackfire mine officials had threatened him.

"This murder dramatically illustrates the terrible situation that confronts human rights advocates both in the state of Chiapas and the rest of the country," said Marie-Dominik Langlois, who heads the non-profit Montreal-based Committee for Human Rights in Latin America, a group that monitors labour practices of Canadian mining firms.

In Chiapas, the Fray Bartolome de Las Casas Center for Human Rights issued a statement condemning Abarca Robledo's murder. The statement said Abarca Robledo was sitting in a van in front of his home on Friday night, talking to a friend when a motorcyclist passing by opened fire.

"We demand that the Mexican government immediately end all acts of aggression and start protecting defenders of human rights," the statement said.

The southern state of Chiapas, rich in oil and gas, was opened to mining concessions about 10 years ago by the federal government.

The leases, mostly held by Canadian firms, have been challenged by residents who are concerned about environmental damage and say they have a right to their own land.