The Brazilian environmental protection agency Ibama said on Wednesday it had rejected a request from state-run oil company Petrobras to drill a well at the mouth of the Amazon River.
The much-awaited decision follows a technical recommendation by the agency's experts to reject the proposal.
Petrobras has for years been trying to open up a new exploration front on the coast of Amapa state in northern Brazil near Guyana, where Exxon Mobil has made important discoveries.
A technical report from Ibama had previously advised against the request, citing discrepancies in environmental studies, inadequate measures for communicating with indigenous communities, and insufficiencies in Petrobras' plan to safeguard the region's wildlife.
Petrobras had several opportunities to solve controversial points of its project, but it was still presenting "worrying inconsistencies" for the operation in a new exploratory frontier of "high socio-environmental vulnerability," Ibama said in a statement.
Petrobras did not immediately respond to a request for comment.
(Reuters - Reporting by Anthony Boadle, writing by Carolina Pulice; editing by Uttaresh Venkateshwaran)