Mexico''s Congress on Wednesday urged the government to cancel Grupo Mexico''s concession to operate one of the world''s biggest copper mines after a toxic spill there earlier this month.

The federal attorney general''s office for environmental protection (Profepa) says the spill pumped 40,000 cubic meters of toxic mining acid into the Bacanuchi river in northern Sonora state.

Profepa said on Monday it would bring charges against Buena Vista del Cobre, the Grupo Mexico subsidiary that operates the copper mine.

Metals miner and railroad operator Grupo Mexico is in the midst of a $3.4 billion expansion project at the mine, which is formerly known as Cananea and has the largest proven copper reserves in the world. The expansion aims to boost production capacity to 1.3 million tonnes by 2017.

The permanent committee that presides over Congress when it is not in regular session urged the economy ministry to "order the cancellation of the concession given to Grupo Mexico regarding the Cananea mine as a result of the ecological damage and the imminent risk the population was subjected to."

It also called on the state of Sonora''s government to suspend activities at the mine.

A spokesman for Groupo Mexico was not immediately available to comment.

President Enrique Pena Nieto said early on Wednesday that damage done by the spill to the surrounding population and environment was high, and added that he assumed small sanctions "would not do."