The local representative of the Agency, Antonio Pereira, said he had spoken to them, compared anthropological data and confirmed beyond any doubt that they were Naua.
A remarkable story of survival has emerged in Brazil, involving an indigenous Indian tribe that was thought to have died out more than half a century ago.
The authorities have identified about 250 people living on a remote mountain range near the border with Peru as members of the long-lost Naua tribe.
An official from the government's Indigenous Affairs Agency said the tribe had been thought to have become extinct in the 1920s.
The discovery of the Naua is part of a resurgence of indigenous peoples which has gathered pace in recent years.
Home of the indigenous
Brazil's north-western jungle state of Acre is one of the remotest places on Earth.
It is home to several of the country's remaining Indian tribes.
But, until recently, no one believed that the Naua still existed, despite the fact that they were once the most populous tribe in the region.
The local representative of the Agency, Antonio Pereira, said he had spoken to them, compared anthropological data and confirmed beyond any doubt that they were Naua.
However, according to Mr Pereira, few of them speak the Naua language and they have lost many of their cultural traditions.
He said that, like all Indian peoples, the Naua will now be entitled to their own reservation. The task will be to demarcate it.
"We thought there were no more Naua," Mr Pereira said. "Our job now is finding them land. No humans are allowed in the park, just the forest and the animals."
Colonialists
When Portuguese colonisers arrived in Brazil in 1500 the country had at least five million indigenous inhabitants.
War, disease and hardship caused that number to drop catastrophically, reaching a low point of about 100,000 in the 1970s.
But since then, Indians have won new constitutional rights and their numbers are growing rapidly.
Some of this can be accounted for by tribes like the Naua, who lost their cultural traditions through contact with white people and have only recently come forward to identify themselves.
It is a trend which is welcomed by anthropologists, who feel that Brazil is rediscovering the strength of its indigenous roots.