LIMA – Peru's government has revoked its authorisation for Southern Copper's Tia Maria copper project and sent it back to authorities for review, the mining ministry said on Friday, creating a new obstacle for the long-stalled project.

Tia Maria, one of the biggest mines under development in Peru, the world's third-largest copper producer, has a target start date of late 2027 following more than a decade of opposition from local farmers and residents who fear pollution and water contamination.

The mining ministry did not say why it revoked permission issued in October for "the start of exploitation activities," but said the new evaluation is aimed at ensuring transparency and legal certainty.

A legal review by the Mining Council declared null a resolution that had authorized the previous start of the operation.

"The file will be returned to the General Directorate of Mining, which will issue a new pronouncement in strict compliance with the guidelines established by the Mining Council and current regulations," it said in a statement.

Southern Copper declined to comment. The company is owned by Grupo Mexico and was Peru's top copper producer last year.

The $1.8-billion Tia Maria project is about a quarter complete and aims to produce 120 000 metric tons of copper a year.

Local farmers and residents have long feared the mine will cause pollution and threaten water supplies. Violent protests against the project in 2011 and 2015 left six people dead and dozens injured following clashes with police.

Peru central bank chief economist Adrian Armas said on Friday he hoped the issue would be resolved quickly, adding that the move should not affect overall investment.

"The project is important for the country," Armas said during a call. "We hope that this issue will be resolved, but the investment projects, specifically the investment updates, continue."

Southern Copper is also developing several other projects in Peru, including Los Chancas and Michiquillay, as part of a planned $10.3 billion investment over the next decade.

The company already operates the Toquepala and Cuajone copper mines as well as the Ilo refinery in southern Peru.