The requirement represents a new obstacle for the company's attempts to drill an exploratory well about 175 kilometers from the country's northernmost coast, amid increased resistance from local indigenous leaders in the state of Amapa.

Brazil's state oil company Petrobras must conduct a series of studies on the impact on indigenous groups in the Amazon region of offshore drilling planned in the vicinity, according to documents from federal and local government agencies.

The extensive studies required by the Brazilian environmental agency Ibama aim to determine the "social, cultural and environmental" impact on indigenous peoples of drilling in the Foz do Amazonas basin, part of the so-called Equatorial Margin.

The requirement for new studies was part of a set of documents sent by Ibama to Petrobras on April 17.

The development is a new obstacle in the company's attempts to drill an exploratory well about 175 kilometers (110 miles) off Brazil's northernmost coast, amid increasingly stiff resistance from local indigenous leaders in the Amapa state.

Petrobras said in a statement that all studies and requirements requested by Ibama in the field of environmental licensing and in accordance with current legislation were addressed. The company added that it is open to incorporate new requests as needed.

The oil giant has stated that drilling in the region would have "no direct impact" on indigenous communities and argued that the time had passed to demand formal consultation with them.

Petrobras CEO Jean Paul Prates has stated that he hopes to begin drilling in the area this year.

However, further studies are likely to take at least six months, according to a person close to the Brazilian indigenous affairs agency Funai.

That may further delay exploration plans for the Foz do Amazonas basin in the Atlantic Ocean, considered Brazil's most promising frontier for oil prospecting because it shares geology with the coast of nearby Guyana, where Exxon is developing huge deposits.

A year ago, Ibama denied Petrobras a license to drill in the area, citing possible impacts on indigenous groups and the sensitive coastal biome. Days later, Petrobras appealed the decision, and has since been waiting for Ibama's response.

In October, Ibama asked Funai to rule on the matter before deciding the appeal. In December, Funai told Ibama that it required several more studies to evaluate the impacts, according to a government document.

On April 17, Ibama sent the memorandum to Petrobras, notifying the company that it had to address it.

"Ibama's understanding is that Petrobras must address these demands," the agency said in a statement to Reuters, adding that a final decision on the appeal would be impossible without it.

Funai declined to give a timeline on how long the studies would take, adding that it depends on the schedule established by Petrobras and a consultancy hired for the studies, which will be presented to the indigenous peoples.

The December Funai memo outlined the requirements for a study to evaluate how the project would affect indigenous communities and their customs, local flora and fauna, and economic activity in the area, which would culminate in a "Feasibility Analysis." 

Funai said that if the project is deemed "viable," the studies will be used to propose "measures to mitigate, control and compensate for impacts, if necessary."

Ibama's decision to require the study proposed by Funai is a victory for the Council of Chiefs of the Indigenous People of Oiapoque (CCPIO), a group that represents the 8,000 indigenous people of the area.

Since 2022, the CCPIO has denounced the effects of Petrobras' activities in the region on indigenous communities, and has demanded a 13-month formal consultation on their views on the project.

CCPIO coordinator Cacique Edmilson Oliveira considers the regulatory decision a victory, he told the news outlet by phone, adding that the studies will provide indigenous communities with greater understanding about what is happening.

"I think it is important to have this data," Oliveira said. "We will not risk any harm."

He added that the oil company will have to take into account that coastal indigenous lands could be threatened by drilling, even though the plan is to search for offshore oil.