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 10-21.

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 organizations 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, told AFP.

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

- Opening the door -

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 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," said Energy Minister Alexandre Silveira in a statement.

Petrobras said it would immediately start drilling an exploratory well at Block 59, an offshore site 500 kilometres (310 miles) from the mouth of the Amazon River.

Environmentalists have raised alarm about drilling for oil 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.

"We hope to obtain excellent results from this research and prove the existence of oil in the Brazilian portion of this new global energy frontier," said Magda Chambriard, president of Petrobras, in a statement.

Brazil meets most of its energy needs through renewables and exports more than half of its oil, so emissions from new oil production won't add to its own greenhouse gas tally, but will still be released globally.

"Authorising new oil licenses in the Amazon is not just a historic mistake - it's doubling down on a model that has already failed," said Ilan Zugman of the advocacy group 350.org

- Risk of 'massive biodiversity loss' -

Ibama denied Petrobras an exploration license in 2023, citing inadequate plans to protect wildlife in case of an oil spill.

As Petrobras appealed, pressure rose from Lula, who said earlier this year that Ibama was a government agency acting as if it was "against the government."

In February, an Ibama technical opinion seen by AFP said the recommendation remained to "deny the environmental license," citing the risk of "massive biodiversity loss in a highly sensitive marine ecosystem."

Ibama's technical staff also noted that drilling conditions were very challenging in the Foz de Amazonas basin, which is prone to intense storms and strong ocean currents.

In May, Ibama chief Rodrigo Agostinho cleared Petrobras to conduct an oil-spill drill, the last step before licensing.

The test exposed gaps in wildlife protection, but Ibama said Monday that another exercise would occur "during the drilling activity."