Despite strong opposition from environmental activists, Petrobas last year was granted a license to explore for oil in the Equatorial Margin, about 500 kilometers (310 miles) from the mouth of the Amazon River.

On Thursday, the company said "a leak of drilling fluid was identified in two auxiliary lines" connecting the drilling rig to a well about 175 kilometers offshore.

Drilling fluid is a liquid used to cool and lubricate equipment during drilling.

The leak "was immediately contained and isolated," and the lines will be brought to the surface for inspection and repair, the company added.

Petrobras assured that the leaked fluid met "permitted toxicity limits," was biodegradable and posed no danger to the environment or public health.

Groups representing environmentalists, Indigenous people, artisanal fishers and Afro-Brazilian communities have gone to court to request an end to the drilling, which they see as a risk to a region rich in biodiversity.

Left-wing President Luiz Inacio Lula da Silva has controversially backed the exploration project, arguing that oil revenues are needed to finance Brazil's energy transition.

At the UN climate conference in November in the Amazon region city of Belem, he was accused of hypocrisy by environmentalists for pushing a "roadmap" for phasing out fossil fuels despite himself backing the exploration of new oil fields.

While Venezuela has the largest known oil reserves in the world, Brazil is the largest oil producer in Latin America, with 3.4 million barrels per day in 2024.

Yet half of its domestic energy comes from renewable sources.

Petrobas is conducting exploratory drilling to assess the feasibility of the field.

This phase is estimated to last about five months.