LISBON - Portuguese prosecutors have asked a judge to annul an environment permit for a lithium mining project being developed by London-based Savannah Resources, alleging various legal infringements, a court document seen by Reuters showed.

The document, filed by the Prosecutor's Office in December and seen by Reuters on Thursday, upheld a lawsuit filed by a municipality in northern Portugal that sought to block Savannah from developing what could become western Europe's largest lithium mine.

Last year Portugal's environmental agency APA gave environmental approval, conditional on some remedies, for Savannah Resources to develop a mine in Boticas, in the Barroso region of northern Portugal, a world heritage site for agriculture since 2018.

The Prosecutor's Office requested that the Administrative Court of Mirandela in northern Portugal annul the environmental approval of the Boticas mine as it "suffers from the defect of violating the law", citing risks "known" to APA that the mine could endanger the heritage site and Portugal's international commitments.

It also said that APA had failed to correctly assess mining waste management needs or water contamination risks, and did not consider the real joint impact from the Savannah mine and another mine being developed by Portuguese mining company Lusorecursos to extract battery-grade lithium in Montalegre, northern Portugal, despite their proximity and large scale.

APA did not reply to a Reuters request for comment.

Savannah said it was "ready to address the concerns" of the prosecutors and cited advice from its lawyers "that the lawsuit is without foundation" and does not impact the project's activities.

The Savannah mine was part of a wider probe last year by Portuguese prosecutors into alleged illegalities in lithium and "green" hydrogen deals.

The probe led to the resignation in November of then Prime Minister Antonio Costa after prosecutors detained his chief of staff and named APA head Nuno Lacasta as a formal suspect in alleged illegalities. Costa and Lacasta have denied any wrongdoing.

Savannah said in January that after a full legal assessment which included due diligence by independent experts of relevant accounts, facts and documents, "Savannah can confidently reaffirm its solid legal standing."

With more than 60 000 tonnes of known lithium reserves, Portugal has been seen as central to Europe's efforts to secure more of the battery value chain and cut reliance on imports.

Catarina Alves Scarrott, a campaigner against mining in Barroso, viewed the prosecutors' move as a victory, but said there was no timing yet for a court decision.