Air surveillance images showed the tribe in the Javari Valley close to the border with Peru, according to Fabricio Amorim of the National Indian Foundation (Funai).
The flights showed four large villages featuring huts and plantings of corn and bananas by the community, Funai said.
"The plantation, as well as the huts, are new, dated to a maximum of one year," said Mr Amorim.
"The state of the straw used in construction and the planting of corn indicate this. Besides corn, there was bananas and a vegetation in undergrowth that appeared to be peanuts, among other crops." The flyovers were carried out after small forest clearings were detected on satellite images, indicating the possibility of human settlements.
Brazilian authorities ban the general population from any contact with the isolated tribes due to concerns that they could easily become infected with diseases for which they carry no immunity.
The region is already threatened by illegal logging, fishing and gold mining operations and by drug traffickers operating in the area, according to Funai officials.
The newly discovered group probably belongs to the Pano linguistic community which lives in the area, Mr Amorim said.
Funai has not established contact with the group but said that the Javari Valley is regarded as having the "highest concentration of isolated groups in the Amazon and the world" and could be home to 2,000 indigenous people from at least 14 tribes.
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