Petrobras said on Monday it had received a license to drill for oil near the mouth of the Amazon River, enraging environmentalists who said the move would undermine Brazil's hosting of UN climate talks next month.

Plans to expand oil exploration in Brazil, already the world's eighth largest producer, are backed by President Luiz Inacio Lula da Silva, who insists oil revenues will help fund Brazil's climate transition.

Critics accuse him of a contradictory stance as he urges world leaders to step up in the fight against climate change ahead of COP30 talks in the Amazon city of Belem from November 10 to 21.

Petrobras was granted a license to drill in the Foz de Amazonas region after a five-year battle for permission to explore the area.

Brazil's environmental agency Ibama said it had given the go-ahead after "a rigorous environmental licensing process."

However, Brazil's Climate Observatory NGO said civil society organisations would go to court to fight the decision.

"The government is sabotaging the leadership it should have at COP30," Suely Araujo, a former president of Ibama and coordinator of the Climate Observatory NGO said.

"How can our diplomats advocate for the shift away from fossil fuels ...when the country is intensifying fossil fuel exploration and production?"

Araujo, who denied French oil giant Total a drilling license in nearby blocks in 2018, said granting the license had opened the door for other permits in the same region.

Foz de Amazonas is part of a promising new offshore oil frontier, with nearby Guyana emerging as a major oil producer in less than a decade following large offshore discoveries.

The region "represents the future of our oil sovereignty. Brazil cannot afford to neglect its potential," Energy Minister Alexandre Silveira said in a statement.

"As long as the world demands oil, someone will supply it... Brazil is going to COP with its head held high," Silveira said in an interview with the Globo News broadcaster.

Petrobras said it would immediately start drilling an exploratory well at Block 59, an offshore site 500 kilometres from the mouth of the Amazon River.

Environmentalists have raised alarm about drilling for oil 160 kilometres off the coast of the world's largest tropical rainforest, which is home to several Indigenous communities.

Petrobras has said its models show that an oil spill at the offshore site "would not be likely to reach the coast" and there would be "no direct impact" on Indigenous communities. (AFP)