A Brazilian Indian who celebrates her birthday on Saturday may be the oldest woman in the world - and by some distance.

Maria Lucimar Pereira, a member of the Kaxinawa tribe, is 121 years old, says a tribal rights group.

It says she has a birth certificate showing she was born in 1890.

But the Guinness Book of Records says she has not been registered with them. The verified oldest living woman is 115-year-old American Besse Cooper.

Maria puts her longevity down to a healthy lifestyle, Survival International said - with regular dishes including grilled meat, monkey, fish, the root vegetable manioc and banana porridge, and no salt, sugar or processed foods.

She has never lived in a city and does not speak Portuguese, only the language of her tribe, the Kaxinawa, which inhabits Brazil's western Amazon and eastern Peru.

She remains physically active, community leader Carlos told Survival - walking around the village telling stories and visiting grandchildren in neighbouring areas.

Maria says she will spend her birthday with her family.

The pictures of Maria were taken by employees of the INSS - the national social security institute - when she responded to a request, broadcast on public radio, to appear at the regional INSS office, Brazilian media reported.

Brazilians over the age of 110 are asked to visit their local offices to prove that they are still alive in order to receive pensions or other benefits.

Guinness World Records told the BBC it had no record of contact from Maria Lucimar Pereira or anyone on her behalf. It said the oldest verified living person remained Besse Cooper.

"We would be very interested in hearing from anyone who believes they are older than this can provide documentary evidence," the company's Damian Field said.

Survival says her birth certificate, which it has a copy of, was issued in 1985.

It paints a picture of the troubles Maria may have lived through, such as the rubber boom which saw many Indians enslaved and killed.

"All too often we witness the negative effects forced change can have on indigenous peoples," Survival director Stephen Corry said.

"It is refreshing to see a community that has retained strong links to its ancestral land and enjoyed the undeniable benefits of this."